Starring Jason Clarke. Rated PG

Ever since George Washington turned down the crown, Americans have claimed that they abhor dynasties. Among all the Bushes, Clintons, Roosevelts, and Romneys, only the Kennedy name has maintained some aura of clan magic. Chappaquiddick doesn’t delve into people-positive efforts “Lion of the Senate” Edward Kennedy championed before dying nine years ago. It focuses on an event that almost ended his life and career, and certainly derailed his chances of being president.

Teddy was only 30 when he took over John’s Massachusetts Senate seat after his brother was elected president. Eldest sibling Joe Kennedy Jr. died in the Second World War, and both JFK and Robert Kennedy would be assassinated in the turbulent ’60s. To say the still-green pol was under intense pressure after Richard Nixon was elected is a serious understatement.

Smoothly directed by John Curran, best-known for his handsome adaptation of The Painted Veil—from a Somerset Maugham novel about a good man whose half-baked idealism proves fatal—this surprisingly sharp-witted film focuses only on July 18, 1969, and the following week. Australia’s big-headed Jason Clarke (Mudbound) is a perfect choice to play the baby-faced senator and Kate Mara is well-matched with Mary Jo Kopechne, on hand for a raucous Kennedy party on Chappaquiddick Island, next to Martha’s Vineyard. She was one of the “Boiler Room Girls” who had worked on Bobby’s presidential bid the year before, and who are referred to here as secretaries, although their efforts as pollsters, statisticians, and speechwriters were the same as their male counterparts’.

First-time screenwriters Taylor Allen and Andrew Logan hint that Teddy and Mary Jo might have had a thing going, or wanted to, and there was certainly alcohol involved that night when he drove his 1967 Oldsmobile off a narrow bridge and into a shallow pond. No one knows how Kennedy got out of the submerged vehicle or why Kopechne didn’t—just that he didn’t report the incident until it was too late to save her.

There’s a hint of suicide right before the plunge, but the alarmingly relevant story is really about how the forces of power gather around an overwhelmed scion of wealth to protect his family “honour”. These are led, remotely, by old Joe Kennedy (Bruce Dern), silenced by several strokes, and enabled by many lesser characters, including police, judges, and prosecutors. It was also a bit of blind luck that Neil Armstrong walked on the moon two days later.

In a rare straight role, Ed Helms plays Kennedy cousin Joe Gargan, a veteran fixer who finally draws the line when he sees Teddy losing the “true compass” he has always bragged about. In the end, this is less a tale about politics or bad character than about creeping corruption—a kind of religion that embraces all denominations.