If not for a strong central performance by Woody Harrelson, director Rob Reiner’s “LBJ” would be a no-hoper: a well-intended but ham-fisted biographical drama of our 36th president, a power broker who turned his uncouth Texas manner into an advantage.

Reiner and rookie screenwriter Joey Hartstone frame LBJ’s story with the day he became president: Nov. 22, 1963, the day when John F. Kennedy (played by Jeffrey Donovan) was assassinated in Dallas and Johnson, JFK’s veep, ascended to the job. Reiner cuts back to Dallas frequently, pumping artificial tension and menace to a dry account of Johnson’s pre-presidential career.

Reiner shows us Johnson as Senate majority leader, a master political player from Texas working to keep a junior senator (Bill Pullman) from his home state in line while also exploring his own run for the presidency in 1960. Johnson’s main rival is Kennedy, and he finds the charismatic Massachusetts senator unstoppable in the primaries and at the Democratic National Convention. Over the objections of his brother Bobby (Michael Stahl-David), JFK offers LBJ a spot on the ticket — a move calculated to deliver Southern states to Kennedy, but also one that deprives Johnson of his Senate power.

Harrelson has his best moments depicting Johnson in the hours and days after Kennedy’s death, showing the public grief and private insecurities at acquiring the Oval Office that way. But Reiner bogs the story in backroom intrigue, as Kennedy’s loyalists argue whether to support Johnson, who’s battling his old Southern ally, Sen. Richard Russell (Richard Jenkins), over his drive to push Kennedy’s Civil Rights Act — a bill that could (and, history tells us, did) alienate the South from the Democrats for generations.

The movie’s ponderous re-enactment of history has the unfortunate effect of putting good actors in thankless roles, often under odd-looking prosthetics. Jennifer Jason Leigh comes off particularly bad in this regard, made up as Johnson’s wife, Lady Bird, with a permanent scowl.

Harrelson, saddled with exaggerated ears and jowls, manages to emit a twinkle or two in his performance. A Texan himself, he deftly captures Johnson’s gruff no-bull attitude and his wheeler-dealer charm, along with the demons that lay underneath. It’s a strong performance, deserving of a more in-depth biography than “LBJ” gives him.

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Woody Harrelson’s performance as Lyndon Johnson is the draw to this dust-covered biographical drama.

Where • Area theaters.

When • Opens Friday, Nov. 3.

Rating • R for language.

Running time • 98 minutes.