A powerful man with sights on the White House behaves atrociously, even criminally. He uses fixers and lawyers and his own charisma to contain the damage and spin the narrative. It works. People shrug off the scandal and vote for him.

No, not Donald Trump, and not the Republicans.

This was Edward Kennedy, the voters were Democrats and the scandal was called Chappaquiddick, after the island in Massachusetts where the young senator drove off a bridge one July night in 1969.

His Oldsmobile flipped upside down into a pond. Kennedy swam to safety. His passenger, a 28-year-old aide named Mary Jo Kopechne, died inside the water-filled car. Kennedy did not seek help at the nearest house nor report the incident to authorities for 10 hours.

The accident and its aftermath are the subject of a new film, Chappaquiddick, which revisits a dark corner of the Kennedy legacy many liberals would prefer to forget.

The scandal wrecked the dream of Teddy becoming president, of carrying the mantle of his assassinated brothers, Jack and Robert, into the Oval Office.

But the voters of Massachusetts forgave him, re-electing him to the Senate until his death in 2009, and the Democratic party establishment forgave him, anointing him conscience of the left, Lion of the Senate.

The Kennedys are once again holding America in thrall. A new six-part CNN series, American Dynasties: The Kennedys, has topped cable ratings. A Netflix documentary about the 50th anniversary of Robert’s 1968 presidential run will unleash fresh nostalgia later this month.

However Chappaquiddick, directed by John Curran and written by Taylor Allen and Andrew Logan, focuses not on glamour, martyrdom or Camelot mystique but a tawdry, boozy weekend gone tragically wrong.

The screenplay, mixing historical detail and dramatic licence, holds up a harsh mirror to the youngest Kennedy brother, played by Jason Clarke, portraying a reckless, privileged princeling with a shaky moral core who pulled strings to escape jail.

It ends with archive television news footage of voters largely exculpating him after the inquest in 1970. “The guy’s a good guy. I’m in favour of him,” says one young man. “There’s more to it than what we know but I actually would vote for him,” says a middle-aged woman.

They were speaking long before Facebook information bubbles, hyper-polarisation and Trump’s boast as a presidential candidate that he could shoot someone and not lose votes.

“In terms of blind loyalty to ‘my guy’ there is some level of similarity in the sense that there is a base of supporters who will follow Trump no matter what he does wrong,” said Thomas Maier, author of two books on the Kennedys.

Trump’s supporters would point out that his transgressions – such as bragging about sexual assault – don’t include a dead body.

Maier, for his part, points out that Kennedy’s behaviour on the fateful night should be put in context of a man who served the nation as a skilled, diligent legislator and was grieving for his murdered brothers when he made a terrible mistake.

“Not to excuse it but when people go through such horrific things they resort to alcoholism and other things they may not otherwise have done. And there was a lot of fidelity to the Kennedys because they had broken through barriers.”

The senator was 37 and eyeing a 1972 White House run when he went to Martha’s Vineyard for a sailing regatta and to party with male friends and the so-called “boiler room girls” – young women who worked on Kennedy campaigns.

He left a party some time before midnight with Kopechne, took a wrong turn down a dirt track, drove off a small wooden bridge and flipped the car into Poucha Pond.

Some details remain murky, prompting conspiracy theories about murder plots, but the widely held view is that Kennedy was drinking and panicked.

At the inquest Kennedy said after escaping the car he called Kopechne’s name several times from the shore and tried to swim down to free her seven or eight times.

He walked back to the party house – past other homes which he may or may not have seen – and with two friends returned to the submerged car and made fresh, unsuccessful recovery efforts. Kennedy then went to his hotel and collapsed in bed.

Fishermen alerted police to the vehicle the next morning around 8.20am. A diver swiftly extracted Kopechne’s body. Kennedy was by then at a ferry crossing pay phone making calls to friends and fixers. He did not report to police until 10am.

John Farrar, the diver, told the inquest Kopechne may have survived for three to four hours, using an air bubble, before suffocating.

Kennedy escaped potential charges of manslaughter, perjury and driving to endanger. He pleaded guilty to leaving the scene of a crash causing personal injury and received a two-month suspended jail sentence.

The scandal killed his White House hopes – he didn’t run in 1972 or 1976 and failed in a 1980 bid for the nomination - but enjoyed 40 more years as a senator, revered and, in the eyes of many supporters, redeemed.

At Chappaquiddick’s premiere in Los Angeles last month, Ed Helms, who plays Kennedy’s confidant Joe Gargan, drew parallels with Trump evading consequences of his behaviour. “What’s really unnerving about the way Trump doesn’t take responsibility for things is that [it’s] hard to hold him accountable for those things.”

At the same event Byron Allen, the comedian-turned-entertainment mogul whose company is releasing the film, hinted that Kennedy allies still sought to dim scrutiny half a century after the tragedy.

“Unfortunately, there are some very powerful people who tried to put pressure on me not to release this movie. They went out of their way to try and influence me in a negative way. I made it very clear that I’m not about the right, I’m not about the left. I’m about the truth.”

• Chappaquiddick is released in US cinemas on 6 April with a UK date yet to be announced