There are two words that are never spoken in Showtime’s recent four-part documentary series “The Reagans”: Donald Trump. But they don’t need to be. “The Reagans” scrapes off the hagiographic goo that’s been spackled over Ronald Reagan since he left office in 1989, revealing the obvious reality underneath: Reagan was Trump’s progenitor, and Trump is Reagan’s degenerate 21st century descendant. Trump is to Reagan much like crack is to cocaine: cheaper, faster-acting, and less glamorous. Still, in their essence, they are the same thing.

This would be common knowledge if the United States had any kind of historical memory. But we don’t.

Take Reagan’s popularity while in office. A collection of perspectives on Reagan published by Stanford’s Hoover Institution just after he left office referred to him as “the most popular of our modern presidents.” History.com tells us he was “a popular two-term president.” The Ronald Reagan Presidential Library and Museum reports that he “consistently received very high approval ratings.”

This is all made up. Of the 13 presidents since World War II, Reagan has only the sixth-highest average approval rating. Both George H.W. Bush, who was a one-term president, and Bill Clinton, who was impeached, were more popular.

What “The Reagans” does extremely well is discard these kinds of fantasies about Reagan, retrieve the basic facts about him, and try to put them back into history. And when we see who Reagan actually was, the degree to which he and Trump share the same political DNA is genuinely startling.

Most obviously, both were entertainers before they were politicians. Reagan was an actor pretending to be a football hero or a war hero. In reality, Reagan wasn’t any good at football and remained quietly ensconced in California for all of World War II. Trump excelled in an even cruder, more deceptive medium — reality TV — in which he pretended to be a successful businessman. In reality, Trump companies have declared bankruptcy six times. If Trump had simply taken the $400 million his father gave him in his lifetime and put it into a mutual fund, he’d have something like $7 billion more today.

Both used their fame to turn themselves into chintzy corporate pitchmen. Reagan sold RC Cola, Chesterfield cigarettes, and Jeris Antiseptic Hair Tonic. Trump was even more shameless, endorsing Trump steaks, Trump vodka, Trump coffee pods, Trump water, a Trump board game, and, least appealing of all, Trump mattresses.

They were both able to use their fame to leapfrog over thousands of sweaty, striving competitors. Barack Obama had to begin as an Illinois state senator, while Clinton started as Arkansas attorney general. Reagan’s first elective office was governor of America’s most populous state, California; Trump went straight to president.

Reagan’s public persona was genial. Yet he had a powerfully cruel, ugly streak that would manifest from time to time. In 1969, police shot dozens of Berkeley demonstrators, killing one. Reagan later snapped, “If it takes a bloodbath, let’s get it over with.” When Patty Hearst’s kidnappers demanded that her family start handing out free food to the poor, Reagan privately said, “It’s too bad we can’t have an epidemic of botulism.” In a phone call with Richard Nixon, Reagan referred to African diplomats as “monkeys.” Of course, this would be just a Tuesday morning on Twitter for Trump, who has the same viciousness but nothing else.

Reagan was the oldest person ever newly elected, at 69 — until Trump won at age 70. (President-elect Joe Biden has now lapped them both, beating Trump just before Biden’s 78th birthday.)

Reagan needed glasses but tried never to wear them in public; the same is true for Trump. Despite Reagan’s age, his hair was always jet black. Ludicrously, Reagan denied that he dyed it, but in fact the same hairdresser who worked on his wife Nancy also took care of his gray roots. Trump dyes and styles his hair to conceal a scalp that, in its natural state, looks something like Darth Vader’s.

Both Reagan and Trump were so manifestly unqualified to be president that their inner circles considered unusual machinations to reassure the public. Reagan almost asked former president Gerald Ford to be his running mate. Trump’s 2016 campaign leaked the news that they were looking for a vice presidential pick who’d be in charge of regular business while Trump would take care of making America great.

Perhaps half of what Reagan said had something to do with reality. The rest originated in the fantasy world in which Reagan spent much of his mental life. Reagan never left the U.S. during World War II, but he once told Israeli Prime Minister Yitzhak Shamir an elaborate story about being a photographer in a U.S. military unit that filmed concentration camps in 1945. Trump has taken Reagan’s tendency to fabulate and expanded it to every single thing he says on every subject.

Finally, both Reagan and Trump were underestimated at every turn by America’s sputtering Democrats. In the weeks before the 1980 election, the race was often seen as a toss-up. Newsweek prepared three possible covers: one for a Reagan victory, one for Jimmy Carter winning, and one if neither won a majority of the electoral vote and the race were thrown into the House. Reagan then won 44 states. It was the greatest shock to the liberal system until Trump’s victory 36 years later.

The question that “The Reagans” raises is why we couldn’t see this about Reagan and Trump from the beginning. Here’s one small but illustrative part of the answer: “The Reagans” isn’t the first program with that title to appear on Showtime. The channel ran a docudrama with the same name, starring James Brolin as Reagan, in 2003. It was originally produced by CBS, but after sections of the script were leaked and attacked by Republicans, CBS foisted it off on Showtime, explaining, “A free broadcast network, available to all over the public airwaves, has different standards than media the public must pay to view.”

In other words, all but the most anodyne versions of the past are sequestered away from the general public. We engage in a kind of organized forgetting and then forget that we’ve done it. With just a single exception, reviews of 2020’s “The Reagans” didn’t mention “The Reagans” that had come before.