So large does Donald Trump now loom that any examination of the US presidency – even one that’s supposedly historical or fictional – is viewed through the shadow he casts. Audiences can’t help themselves. No matter what point the director or novelist might be making, the viewer or reader is running a silent mental comparison with the current occupant of the White House.

That tends to produce one of two results. Either we see the presidents of the past as paragons of strength and wisdom when judged alongside the foot-stamping narcissist – part toddler, part predator – who sits in the Oval Office today. Or else we see in those long-gone administrations the seeds of Trumpism and the roots of our present trouble.

Both conclusions can be drawn from The Reagan Show, a 75-minute documentary made by Sierra Pettengill and Pacho Velez for CNN Films that consists entirely of archive footage from that era, including outtakes and candid fly-on-the-wall moments collected by an in-house initiative then called White House TV. The film tells us that this effort, which seems to have kept the camera running through every Reagan media appearance or photo-op, gathered more video than the previous five administrations combined.

What turned Trump from a joke in the gossip columns into a national figure were his seasons as TV’s boardroom supremo

The Reagan Show certainly gives plentiful hints that it is telling the story that contains the origins of the Trump odyssey. The film closes with a commentary by the ABC News anchor Peter Jennings, delivered just as Reagan was leaving office. “No presidency before this one was so often judged as if it were a performing art. I shudder when it’s suggested that politicians who come after him will have to succeed first on television.”

That sentence resonates because, of course, it was television that carried Trump to the White House. We may describe him as a real estate tycoon or a business magnate, but the truth is, Trump was a failure as a businessman – deeply indebted and perennially on the verge of bankruptcy. What saved him, what turned him from a joke in the gossip columns of the New York tabloids into a national figure, was his 14 highly rated seasons as the boardroom supremo in The Apprentice. In this sense, Trump was not really a corporate magnate at all: he just played one on TV.

This echoes the critique of Reagan that was a constant refrain in the 1980s. That he was not a real politician, but rather an actor playing one on TV. Critics would make much of Reagan’s use of a teleprompter, suggesting he was reliant on “cue cards” or even the occasional nudge from his wife. (We see again that moment when, as Reagan was lost for words before a group of reporters and cameras, Nancy murmured helpfully, “We’re doing all we can.” He repeated the line immediately.) In this version, the Reagan presidency was merely the final act in a showbusiness life, a Hollywood has-been handed the ultimate final role.

Watch the official trailer for The Reagan Show.

Supporting evidence comes from TV news reports of the time, including one from then White House correspondent – and now Fox News anchor – Chris Wallace, who quotes senior administration officials telling him that Reagan was “disengaged,” on vacation for one out of every six days of his presidency, and that only one third of his time was devoted to “shaping policy” while two thirds went on “ceremony and PR”.

Naturally, these are all observations that could and have been made about Trump. Administration officials today tell reporters that the president is similarly inattentive, preferring to get his information from Fox & Friends rather than from the daily intelligence briefing. As for downtime, the equivalent stat is that Trump has spent roughly one in every five days of his presidency playing golf. As if to amplify the echoes, we see Reagan at a podium giving a ringing incantation of a slogan not yet born. “Make America Great Again,” he says.

Even if the parallel is not as direct as that snippet might suggest, one can at least see the line of descent from that White House to this one. Reagan was a master of the medium of television and that talent – they called him the Great Communicator – was central to the success of his presidency. He could be natural and folksy in front of the camera, speaking with a grandfatherly twinkle, or else rousing and epic, if that’s what the script required. He was the commanding sheriff when he stood at the Brandenburg Gate in 1987 and demanded “Mr Gorbachev, tear down this wall” (a clip that makes it into The Reagan Show). But he could also be the soothing town elder, as when he addressed the nation after the loss of the Challenger space shuttle a year earlier, mourning the astronauts who had “slipped the surly bonds of Earth to touch the face of God” (a highlight missing from this showreel).

A facility on TV had been important since John F Kennedy, but Reagan made it an essential requirement of the job. The documentary opens with a telling exchange between Reagan, nearing the end of his presidency, and the veteran TV anchor David Brinkley. The newsman asks how relevant Reagan’s earlier career as a movie actor proved to be for the role he was about to leave. “There have been times, in this office,” says Reagan, “when I’ve wondered how you could do this job if you hadn’t been an actor.”

In all seriousness … Donald Trump in the Apprentice USA, 2005. Photograph: BBC

Sure enough, his successor, George HW Bush – briefly glimpsed in the film as Reagan’s vice-president – struggled in the top slot, and failed to win a second term, in part because he and the camera didn’t get along. He was famously wrong-footed by an autocue, reading out loud a speechwriter’s instruction intended as a silent stage direction: “Message: I care.”

The men who followed Bush – Clinton, Bush Jnr and Obama – were all more comfortable in front of the camera. But Trump, like Reagan, is a TV professional. True, his genre is different: reality TV thrives on conflict, surprise and rough edges rather than the white bread smoothness and polish of 1950s television, Reagan’s natural milieu. But Trump has mastered the mass media of his age just as surely as Reagan mastered his. Then it was radio and B-movies; now it’s reality TV and Twitter. But the deep affinity is similar.

And yet the differences between them are instructive. True, The Reagan Show lingers on the stagecraft that went into making his presidency look as good as it did. Each photo op was meticulously staged, in what was then a relatively new discipline. We see Michael Deaver, Reagan’s chief image maker, at work, putting his star into settings that would project him as a movie-style hero. (That shot of the president and first lady on horseback at their ranch in California was no accident, but as meticulously produced as one in a David Lean film.)

But, for all that, there was much more to Reagan than a rapport with the lens. The documentary doesn’t show it, but he undertook a transition from showbiz to politics and it was the work of several decades. Reagan was the leader of the stars’ trade union, the Screen Actors Guild, in the late 1940s and into the 50s, a period of strained relations between workforce and management. And, of course, he was a two-term governor of California, leading a state with the population and economy of a serious country.

There is no hint of that pre-presidential political career in this film, but its relevance is obvious: it means the parallels with Trump diverge before they even begin. The current president walked off the set of The Apprentice via the campaign trail into the White House, with no experience of elected or public office along the way. Reagan may have been an actor, but he was a politician for much longer.

Meticulously staged … President Reagan with George Bush, left, meets with General Secretary Mikhail Gorbachev and, far right, interpreter Pavel Palazchenko in 1988.

Still, that’s not the contrast The Reagan Show invites nor is it the one that matters. Unexpectedly, and rather unevenly, the gaze of the documentary eventually settles on Reagan’s relationship with Mikhail Gorbachev and especially the steps the two men took towards nuclear arms control.

We see that in Gorbachev, Reagan had met his match: the Soviet leader was nearly as accomplished in front of the cameras as he was. But we also see that Reagan rose to the moment, and the opportunity, Gorbachev presented. Facing down bitter criticism from the American right – including several Fox-type talking heads who are still active – Reagan pressed on in pursuit of limitations on, and eventual reductions in, the US’s nuclear arsenal. Having once railed against “the evil empire”, Reagan’s animating purpose towards the end of his term was, he said, to “strive for peace”.

One shouldn’t sugarcoat it. Reagan’s presidency was no march of social progress: inequality increased and many advances towards justice were reversed. But still, it’s striking to note that when confronted with the facts of the arms-for-hostages deal with Iran, he did not accuse the press of spreading “fake news”, but went on TV to admit that his earlier account had been untrue.

When the Ku Klux Klan planted a burning cross on the lawn of an African American family in Maryland, Reagan did not praise the KKK as including “some very fine people”, but went to visit, and stand with, the black family whose home had been violated.

Put simply, they might both be Republican presidents who owed their political success to their skill in front of the camera, but the current man is a pygmy next to his predecessor. As this film makes clear, and to adapt a formulation from a different contest: Mr Trump, you’re no Ronald Reagan.

• The Reagan Show is released in UK cinemas on 6 October.