In 1991, when Gabriella Blum was 16 years old, the Israel Defense Forces suggested she go see the world. She’d skipped first grade and subsequently graduated high school in Tel Aviv early — too early to start the mandatory military service all Israelis begin at 18. So the IDF told her to check out Chiang Mai and Mumbai, and to call them in two years. Instead, she joined the IDF’s Academic Reserves, which allows young Israelis to study toward law degrees and eventually work as IDF lawyers. “It was kind of my version of, ‘I was young, I needed the money, who are you to judge me,’” she said, smiling. “That’s how I ended up in law school.”

Blum was a city kid from a left-leaning household. Her father was a physicist, her mother a literature professor. In 1995, when she completed her degree at Tel Aviv University and joined the IDF’s International Law Department, she became the highest-ranking soldier in her family’s history. At the time, the ILD was located in a small office just outside the Kirya, the IDF’s imposing central Tel Aviv headquarters. Blum had gone through basic training, and although she wasn’t obligated to carry her M16 rifle regularly — “It was much safer for everyone that I didn’t” — she interrogated the legality of the army’s actions while clad in her cream-and-olive-green officer’s uniform.

“The tzahal” — the Hebrew acronym for the Israeli army — “lets very young people do things that are outrageous to let a young person do,” Blum says now. “It’s much more apparent when you let a 19-year-old lead other people in battle. But it’s also true for young lawyers. In my unit, we were exposed to some of the most pathbreaking issues. On targeted killings, we were basically pioneers.”

In 2000, when Blum was 25, the Second Intifada, or Palestinian uprising, erupted. That summer, President Bill Clinton’s Camp David peace accords collapsed. Within a few months, Ariel Sharon, then an inflammatory candidate for prime minister, visited Jerusalem’s Temple Mount, the Muslim holy site that historically had been off-limits to Jews. The incitement set off a half-decade of Israeli-Palestinian clashes; hundreds of casualties, primarily Palestinian, were to come. By the end of 2001, Hamas and Islamic Jihad suicide bombers were regularly targeting Israeli malls, pizza shops, bus stops, and nightclubs.

“International law progresses through violations.”

It was within this tragic, fraught climate that the IDF ramped up its targeted killings. As carried out by the Israelis, these were attacks — using small arms as well as manned and unmanned aircraft — on individuals deemed high-level terrorist operatives who were active in the occupied territories of Gaza and the West Bank. Effectively, they were assassinations.

At the time, the U.S. position on these killings was unequivocal. As Martin Indyk, then the U.S. ambassador to Israel, put it in July 2001: “The United States government is against targeted assassinations. … They are extrajudicial killings, and we do not support that.”

A few months before Indyk’s statement, former U.S. Sen. George Mitchell led an international commission to Israel to compile a report on the crisis. While carrying out his investigation, Mitchell and his team met with members of the ILD. Pnina Sharvit Baruch, then-deputy head of the ILD, recalls the senator explaining, “’Terrorists are criminals,’” not enemy combatants. “‘All you can do is arrest them’” — not kill them. “They were very critical of the way we fought. And we said, ‘OK! We disagree!’” she said.

Daniel Reisner, then-head of the ILD, added, “The U.S. administration strongly recommended — not to say urged, not to say instructed us” — to stop the targeted killings.

Then came the 9/11 attacks and, with them, the sudden and now seemingly irrevocable U.S. government position that terrorists must be annihilated by any means necessary. In the 17 years since the attacks, the U.S. has conducted at least 850 targeted assassinations in Pakistan, Yemen, and Somalia alone, killing between 4,100 and 6,200 people, according to the Bureau of Investigative Journalism. Between 600 and 1,250 of those are thought to be civilian deaths.

U.S. targeted killings are often carried out by drones. And under the Obama administration, the Justice Department justified its drone warfare by explicitly citing the legal arguments that Blum and her colleagues developed in that tucked-away ILD office many years ago.

“If you do something for long enough, the world will accept it,” Reisner boasted to Haaretz in 2009. “International law progresses through violations. We invented the targeted assassination thesis, and we had to push it.”

By 2009, such killings were “in the center of the bounds of legitimacy,” Reisner said. “We wrote a revolutionary opinion.”

After her first five years in the ILD, Blum would come and go from the IDF and American academia, piling up advanced degrees. In the mid-2000s, Harvard University hired her to teach at its law school. Now Harvard’s Rita E. Hauser Professor of Human Rights and Humanitarian Law, she has published books and lectured in Switzerland, the United Kingdom, and Italy.

On an agreeable summer afternoon in June, I went to Cambridge to meet her. Nearly two decades ago, she helped hash out the details of targeted killings. Now, she has reservations.

Looking back to the dawn of the Second Intifada, Blum said, “Nobody knew what was going on. Nobody knew what the relevant laws were. You have a conflict in an occupied territory. Is it an international armed conflict between states? But Palestine is not a state, as far as Israel is concerned. It doesn’t look like traditional law enforcement. But if you call it a war, what kind of war is it? A civil war? A new kind of war?”

On December 31, 2000, a Palestinian dentist named Thabet Thabet was shot dead in his West Bank hometown, Tulkarm, by IDF snipers in broad daylight. Thabet was known as a pro-peace figure in the Fatah party, and his death generated consternation in both the Israeli and international press. According to later Israeli government accounts, Thabet was actively involved in terrorism as a leader in Fatah’s armed militia, Tanzim. The immediate question, though, went beyond Thabet’s culpability. The immediate question was: How can you shoot someone, mafia-style, in the street? How can this be legal? That’s when the IDF’s chief of staff called the ILD.

Reisner, Sharvit Baruch, Blum, and a few other ILD colleagues took the lead in answering the question. In war, “you’re not obliged to only target people who take a meaningful part in hostilities,” Blum explained. “Any member of the armed forces is a legitimate target. You can shoot them in the back while they’re sleeping. The only relevant obligation, really, is to minimize civilian casualties.”

The ILD wasn’t ready to grant the Israeli army all the privileges of a war paradigm. But they acknowledged that the situation had deteriorated beyond a policing paradigm. Later, Sharvit Baruch told me, Reisner “coined the terminology ‘armed conflict, short of war’ — which, legally, has no meaning. But it somehow, I think, described our feeling.” Reisner said, “We actually developed — and I am probably to blame for that — the concept of an armed conflict between a state and a nonstate entity.” Decades into the war on terror, that legal concept has become an international commonplace.

Blum recalled the hypotheticals tossed around in the ILD offices: “How good does your information have to be? And who gets to authorize these things? What about a 15-year-old wearing a Hamas uniform and throwing a Molotov cocktail? Or a stone? Does that make him targetable?”

“I’ve jokingly said, ‘For this, I went to law school? To write an opinion on when you can kill people?’” Reisner told me. “But in reality, this was the ultimate question you can ask a military lawyer. We treated this with almost religious reverence.”

“We actually developed the concept of an armed conflict between a state and a non-state entity.” Decades into the war on terror, that legal concept has become an international commonplace.

The discussions were animated, but in Blum’s recollection, always professional. The politics of those in the room ran the spectrum. But these were lawyers, at the end of the day, and they worked for an army. The soundest legal arguments, not the most humane, would win.

“You had to make stuff up as you went along,” Blum said. “Not in a manipulative way. Not, ‘OK, let’s come up with a story that justifies everything we do.’ But we did feel like we were in a different reality. This blending of combatants and civilians in an occupied territory — this was not something that the history of the regulation of war had fully anticipated.”

The new technologies complicated things further. “It was kind of freaky that you’re using this thing,” Blum said. “Drones? It’s a machine? And nobody can surrender to that machine?”

Blum and her fellow lawyers knew they were giving legal cover to actions for which soldiers could be held criminally responsible. A few years before the onset of the Second Intifada, the International Criminal Court had been established in the Hague. Israel never ratified the Rome Treaty, the multinational agreement that created the court. Still, “there were growing concerns about the whole kind of ‘universal jurisdiction’ atmosphere,” Blum said.

That was just one of many pressure points. “It’s emotional,” she explained. “You want to serve the security needs of people who tell you, ‘This is absolutely crucial for our operations.’ You are also a guardian of the law. And in the beginning, we’re also politically alone — nobody likes this! Everybody around the world is sort of, ‘Ughhhhh — we’re not sure this is OK.’ There was concern and confusion and determination to make this work. The entire world is looking. You wanted to get this right.”

Eventually, the ILD established principles to guide the IDF’s targeted killings. The aim was to define the practice as an exception to the norm — a means of last resort.

Their first rule was that targeted killings were not to be used against just any member of an armed group, but only against those who took direct and active roles in hostilities. (Practically speaking, that meant that the commander who ordered the suicide bombing was a valid target, but that the technician who built the bomb itself was not.) Where arrest was a feasible alternative, targeted killings were not to be used. (“That had zero precedent,” Reisner said. “A total invention. It sounds like law enforcement, right?”) And finally, every effort had to be made to avoid civilian injury and death.

The ILD handed its principles to the attorney general, who approved them without pushback and gave them to the IDF as legal guidelines. Then the ILD had to defend those guidelines in court.

In January 2002, the Public Committee Against Torture in Israel, or PCATI, a human rights organization, brought a petition against the IDF’s targeted killings in Israel’s High Court of Justice. Chief Justice Aharon Barak agreed to hear arguments from both sides.

Recalling PCATI’s petition against the ILD and the Israeli government, Blum spoke with clear respect. She summarized the human rights group’s legal argument this way: “Look, we all know that Israel has been assassinating people around the globe for a very long time. This is part of our thing. This the shtick of the Mossad” — Israel’s elite intelligence agency that has famously, and sometimes ineptly, murdered alleged enemies of Israel in sovereign states. “‘There are movies about it! We all know, and we’d never have brought a petition against that. It’s one of those dirty things that governments do in the dark. It’s not nice, it’s not clean, but we’re not going to go there.”

“But this” — the targeted killings program — “is different. This is routine. This is policy. It’s out in the open. And in it’s our backyard, in the occupied territories. Are you allowed to do this?”

As the PCATI petition slowly wended its way through the High Court, with the Intifada roiling in the streets, public opinion on targeted killings was also evolving.

In an infamous incident in July 2002, the IDF killed the Hamas military leader Salah Shehade by dropping a one-ton bomb on his home in a densely populated neighborhood of Gaza City. The bomb killed Shehade along with 13 civilians, eight of whom were children. The result was horror and a small internal mutiny. IDF Air Force pilots, practically demigods in Israel, were attacked as war criminals. A prominent group of Air Force pilots went so far as to declare that they would no longer participate in military strikes on Palestinian cities.

In the first five years of the targeted killings program, according to PCATI, the IDF assassinated roughly 300 terrorist operatives. Those operations also killed 150 civilians and injured hundreds more. The outrage over the Shehade killing is a reminder that targeted killings were not always viewed as normal, even in Israel, and that civilian casualties in “armed conflict, short of war” weren’t so readily accepted, either.

For proponents of targeted killings, however, the theoretical dangers of not carrying them out were easy to explicate. Within a year of the Shehade operation, the IDF obtained intelligence that a “dream team” of upper-echelon Hamas leadership was gathering for a meeting. Purportedly influenced by the lessons of Shehade, the army sent an F-16 to launch a single missile through a third-floor window, where the meeting was believed to be taking place. In fact, the meeting was on the ground floor of the house. The Hamas leaders all survived.

As Avi Dichter, the head of Israel’s internal security service, Shin Bet, at the time, told the journalist Ronen Bergman in an interview for Bergman’s recent, massive history of the Mossad, Shin Bet, and Israel’s decades of assassinations, “Rise and Kill First”: “I wouldn’t dare to count up the number of Israelis who were killed and wounded due to the decision not to blast the whole house.”

In 2006, the High Court finally ruled on the PCATI case. The court embraced the ILD’s arguments, but Barak carved out one additional condition. He stated that the duty of proportionality had to be translated into a bureaucratic process. A military committee would be formed to review targeted killings that resulted in civilian casualties; that committee would be tasked with determining consequences and possible reparations. (The committee exists to this day, but its decisions are not made public.)

That meant that attempts to minimize civilian casualties were being codified. But it also meant that there were no hard rules about how many civilian casualties were too many.

In his ruling, Barak quoted Cicero: “Laws are silent in times of war.”

“These statements are regrettable,” Barak wrote, with high-minded flourish. “It is precisely when the cannons speak that we need laws.”

And then, immediately after: “It has therefore been decided that it cannot be determined ab initio that every targeted killing is prohibited under customary international law, just as it cannot be determined ab initio that every targeted killing is permitted under customary international law.”

Effectively, Barak was saying that every targeted killing had to be weighed on its own legal merits. That meant that every proposed targeted killing was, at least theoretically, legal.

“And that,” said Blum, “has been the governing legal arrangement under which Israel has carried out targeted killings ever since.”

And not just Israel. The George W. Bush administration pointed to the IDF’s precedent in the wake of 9/11 as they pushed the authorization for use of military force, or AUMF — which the U.S. has used to wage its war on terror against Al Qaeda, ISIS, and any future “associated forces” — through Congress. As the New Yorker reported, “Bush’s legal advisers modelled their rationale on Israel’s position against terrorism, arguing that the U.S. government had the right to use lethal force against suspected terrorists in ‘anticipatory’ self-defense.”

In 2007, writing in the Yale Law Journal, Kristen E. Eichensehr, now a professor at the University of California, Los Angeles law school, called the Israeli High Court’s decision “the first authoritative judicial treatment of targeted killings” and warned that it was “likely to influence … the United States—the only state besides Israel to conduct targeted killings openly.” She went on: “The Israeli court’s laxer definition … may be exploited. … What state would have the moral fortitude to be the last adherent to a strict definition of necessity?”

The Obama administration answered that question in 2010, in a Justice Department memo justifying the targeting of the jihadi propagandist Anwar al-Awlaki, an American citizen. The memo directly quotes the ILD’s argument in the PCATI case. “Although arrest, investigation and trial ‘might actually be particularly practical under the conditions of belligerent occupation, in which the army controls the area in which the operation takes place,’” the memo reads, “such alternatives ‘are not means which can always be used,’ either because they are impossible or because they involve a great risk to the lives of soldiers.” A U.S. drone killed al-Awlaki in September 2011 in Yemen.

The next year, then-Attorney General Eric Holder gave a speech at Northwestern University School of Law implicitly defending America’s targeted killings program. In his justification, Holder echoed many of the principles that the ILD had laid down roughly a decade earlier. Targeted killings would only happen when “the individual poses an imminent threat of violent attack” and “capture is not feasible,” he said, and would only be “conducted in a manner consistent with applicable law of war principles.”

On the topic of the Holder speech, Reisner cracked, “I could sue him for plagiarism!”

Of Israel’s stated influence on America, Blum said, “There were certainly conversations unofficially with Americans way before” the al-Awlaki memo. “They were very aware of the PCATI opinion.”

Blum echoed Reisner’s sense that the Israeli court ruling was “revolutionary.” “You’ve charted new territory, and you’re hoping that you’ve charted it in the right way,” she told me.

Blum recalled thinking, then, about “all the unintended consequences that this can have.”

The Harvard Law School quad is a pristine open space tucked away, just down Massachusetts Avenue, from the totemic main campus. Around the sand volleyball courts and steel-pole art installations, students pore over thick texts. On the day I visited, at least one man was pacing around, lost in thought, his arms clasped behind his back.

The buildings have names. Blum’s corner office is on the second floor of Hauser, a granite and dark wood structure surrounded by greenery. She sits at her desk in front of shelves stuffed with hundreds of books, almost all of them featuring some variation of the words “combat,” “battle,” or “war.”

Blum has a breezily dominant way of speaking; she never quite switches off her classroom voice. She seems patient, up to a point, and diligent. On the day I meet her, she is dressed mostly in black.

Blum and her ILD colleagues were clear in their guidance that targeted killings should always be the exception, never the rule. Now she feels that critical checks on the practice have evaporated. “What troubles me most is that the exception has exceeded its logic.,” she said. “The logic was, ‘I’m going to use it sparingly, against the most high-level people, only when I have no alternative.’ That doesn’t seem to be the case anymore.”

Assassinations weren’t intended to be part of a menu of options offered to the military, leaving commanders free to select the most convenient killing method. “That’s the problem when you approve an exception: The exception ends up swallowing the rule,” Blum said.  “All these extraordinary measures that you hope will remain extraordinary — the risk is always that they become a little less extraordinary. And especially if the lawyers told you it’s legal! And if it’s legal, why wouldn’t you do it? But we often confuse what’s legal with what’s moral and what’s wise.”

Blum recalled what the ILD had told the High Court: “‘This is not a punitive tool. This is not instead of putting someone on trial or incarcerating them.’ You need information that connects them to a threat right now, beyond affinity, beyond ideology, beyond whether they like us or not,” she said. “And I don’t know how many of the people that were killed were actually that close. When you look at the American scale, it’s obvious that that can’t be right.”

Blum now believes that “targeted killings became one of the things [Israel] did. Not even really to affect Hamas’s future capacity, but to show that you’re doing something. You’re the Israeli leadership. People are being killed in restaurants and cafes and shopping malls and on buses. You have to do something!”

Given the green light to act, the IDF brass didn’t hesitate. “Somebody needs to stop them and tell them, ‘No, this is going too far. We’re doing too much of this,’” Blum said.

“We often confuse what’s legal with what’s moral and what’s wise.”

It’s been years now since Israel has regularly used targeted killings. As Reisner points out with a bitter levity, regular combat with Hamas in the Gaza Strip means the two sides have had “ample opportunities to shoot at one another directly.” And when Israel does conduct assassinations, they are almost always in Gaza, its direct area of combat. In practice and policy, however, the U.S. drone program has effectively declared the privilege to hit anyone, anywhere. And under the Trump administration, that drone war is only escalating. According to the Bureau of Investigative Journalism, in Trump’s first year in office, the number of strikes carried out in Yemen and Somalia tripled the number that were carried out in Obama’s last year as president; the CIA — working out of a new $110 million base in Dirkou, Niger — is now expanding drone missions in Africa.

As the years pass, Blum suggests that any number of unconventional drone victims may emerge. Americans might target drug traffickers in Afghanistan. A future Mexican president might target heads of cartels. Why wouldn’t the Chinese government go after dissidents internally? And why wouldn’t the Russians go after dissidents everywhere? The only thing that’s certain about targeted killings, Blum says, is that “there’ll be more of them.”

“Do you feel responsible?” I asked. “Personally responsible?”

“No,” she said. “These were the right legal answers to a real problem we were asked to address. It is right — if somebody poses a direct threat to you, and there is no other way to stop them, the right thing to do is kill them. I don’t regret those decisions.” But, she acknowledged, “Every time you come up with a legal theory, the problem is, that legal theory is no longer yours.”

She says targeted killings have eclipsed their original stated purpose. “I don’t feel responsible for that. Even though I’m sure I am.” She paused. “No. That part doesn’t weigh on me morally.”

There’s a quote from the Talmud that the Israelis like to reference when talking about targeted killings. Tractate Sanhedrin, Portion 72, Verse 1: “If someone comes to kill you, rise up and kill him first.” Bergman, the journalist, paraphrased the quote for the title of his recent book. Barak, the chief justice, also quoted from it in his original ruling on the PCATI case.

In her Harvard office, Blum speaks the phrase in Hebrew — “Ha-ba lehorgecha, hashkem lehorgo” – only to discount it. “That doesn’t move me,” she said. “It’s catchy. But look: You and I, we walk down the street, we hope we’re safe. But we know there are risks out there. And that has to be true for any country and for any political entity on the international stage.”

“There’s a way of thinking about all of war as an exercise in allocating risk. Targeted killings are exactly that: an exercise in risk-shifting. The United States targets Mr. X in Yemen to disrupt his threats. Now, maybe those actions do harm to the Yemeni population. But we say, the U.S. is allowed to protect itself.”

“At some point, you have to say, we live in an international society, which means we are exposed to risk. That’s true for Israel. That’s true for the United States. No one is immune. How safe can you seek to be? And at what expense to others? There’s got to be a limit in how you address risk. There’s got to be a limit in what you’re allowed to do.”

Correction: October 8, 2018
A previous version of this story stated incorrectly that Blum quoted a phrase from the Talmud in Aramaic. The quote – “Ha-ba lehorgecha, hashkem lehorgo” – is in Hebrew. 

Top photo: Gabriella Blum.