Democratic Sen. Kamala Harris of California suspended her presidential campaign on Tuesday. Why? Because, she said, she did not “have the financial resources we need to continue. I’m not a billionaire. I can’t fund my own campaign.”

Meanwhile, former New York Mayor Michael Bloomberg, who definitely is a billionaire, has spent at least $57 million of his own money since he jumped into the race on November 24. Harris, by contrast, raised $36 million as of her last campaign filing in October. Of that, she’d spent almost $26 million since she announced her campaign last January 21.

The divergence in the fates of the two candidates can be traced back to a Supreme Court decision on the constitutionality of campaign finance law. But the case involved is not Citizens United v. Federal Election Commission, from 2010. It’s a far less famous one: Buckley v. Valeo, from 1976. The decision opened the door for billionaires — and, more generally, the ultra-rich — to spend as much as they want on their own political campaigns.

The divergence in the fates of Harris and Bloomberg can be traced back to a Supreme Court decision — not from Citizens United in 2010, but Buckley v. Valeo in 1976.

One of the main forces behind the case was a young Republican lawyer named John Bolton, later to become President Donald Trump’s national security adviser for a time. In Bolton’s memoir, he proudly states that “Everyone knew the decision in Buckley v. Valeo could determine … the future shape of American politics.” Bolton was right — and his long-ago efforts continue to bear fruit today.

No Limits

Watergate was, among other things, a scandal about money in politics. President Richard Nixon’s 1972 reelection campaign had accepted bribes, including $200,000 from the chairman of the board of McDonald’s in return for permission from the federal government to raise the price of their Quarter Pounder cheeseburger. (You can read about this here; it’s #21 in the bill of particulars supporting the articles of impeachment against Nixon.)

Soon after Nixon resigned in 1974, Congress responded with significant amendments to the Federal Election Campaign Act. This included a new limit of $50,000 per calendar year on what presidential candidates could spend of their own money on their campaign. Adjusting for inflation, that’s about $275,000 today.

Just two years later, however, the Supreme Court struck that limit down in the Buckley case. Those running for political office could now spend any amount of their own fortune they wanted. In fact, the court stated, it could be good for the wealthy to self-fund runs for office, because “the use of personal funds reduces the candidate’s dependence on outside contributions and thereby counteracts the coercive pressures and attendant risks of abuse.”

The result of the case is a presidential field where billionaires can hang on seemingly forever without batting an eye and other competitors must strain to keep up by raising funds the old fashioned way: through regular, limited donations and by getting billionaires to give to their dark-money groups.

Kamala Can’t Compare

Kamala Harris is quite rich. Forbes estimates the net worth of her and her husband at $6 million, putting them in the top 2 percent of U.S. households. But in 2016, the campaigns of Hillary Clinton and Trump raised $564 million and $333 million, respectively. As Harris said, she can’t fund that by herself.

Bloomberg’s $57 million in ad buys in the 11 days since he announced are already more than twice as much as all Harris’s reported expenditures.

She also can’t get it funded by one super-wealthy supporter. This isn’t because she’s unpopular among billionaires — just the opposite, in fact. Harris has received donations from 46 billionaires and their spouses, more than any other candidate. But while the Supreme Court struck down limits on how much any politician could spend of their own money, it simultaneously upheld limits on donations to candidates from others. The maximum anyone can give to a presidential campaign this cycle is $2,800 for the primaries, and $2,800 for the general election. Through these comparative drips and drabs, Harris raised her relatively paltry $36 million.

By contrast, Bloomberg has an estimated net worth of $54 billion — 9,000 times that of Harris. His $57 million in ad buys in the 11 days since he announced his candidacy are already more than twice as much as all Harris’s reported expenditures.

Viewed another way, Bloomberg so far has spent about $5 million per day. CNBC estimates that Bloomberg may pour $500 million into his campaign by the February 3 Iowa caucuses (Bloomberg plans to skip Iowa as well as the New Hampshire primary). That would be almost 2,000 times more than he could have spent if the Buckley decision had upheld the annual $275,000 limit on a candidate’s donations to his or her own campaign.

Billionaires Everywhere

Bloomberg isn’t the first billionaire to fund his own presidential campaign; he’s not even the only billionaire running in the Democratic primaries. As of October, former hedge fund manager Tom Steyer had given $48 million to Tom Steyer for President. His campaign shows no sign of slowing down, even as the most recent national poll showed him to be the choice of zero percent of voters.

Then there’s obviously Trump, who did not totally self-fund his 2016 campaign. He provided $66 million, or one-fifth, of its total cash, but his campaign likely would never have gotten off the ground if he’d been forced to abide by the pre-Buckley laws.

Money isn’t everything. It seems likely that the main result of Bloomberg’s candidacy will be several fancy new beach homes for his consultants. Mitt Romney spent $45 million of his fortune on his 2008 presidential bid, but lost the Republican nomination to the late Sen. John McCain, R-Ariz. (Romney subsequently spent just $52,000 of his own money in 2012 and did become the nominee.) Steve Forbes expended about $100 million on two humiliating races for president in 1996 and 2000. Even the most successful super-rich candidate before Trump, Ross Perot, came up short.

Nonetheless, there’s no question that Harris would still be in the race if she were a billionaire and, conversely, that the political landscape would look far different if this aspect of the Buckley decision had gone the other way.