Lyndon Baines Johnson is finally getting his dramatic due. After decades of being dismissed pretty much as a vulgar shadow of his martyred predecessor, or even worse as the clueless architect of the Vietnam debacle or a conspirator in JFK’s assassination, he appeared in “Selma” as a canny, if somewhat unprincipled, partner of Martin Luther King, Jr. in advancing the cause of civil rights, and then in Bryan Cranston’s one-man show “All the Way” as a political force of nature who accomplished an incredible amount of progress, despite his failings. Now Rob Reiner offers what amounts to a reverential biography of the man, which might be described as “warts and all” but implies that the warts themselves were a part of what made him great.

“LBJ” isn’t in any respect cinematically innovative. It’s as conventional as they come, the sort of well-meaning, competent but essentially unimaginative biopic that might have been made for television. That’s not to say the movie is uninteresting; it will certainly hold your attention—especially, perhaps, if you lived through the events of the early 1960s. But in the final analysis it’s a fairly ordinary American political docu-drama.

It’s also, as far as the biography goes, incomplete. It ignores Johnson’s earlier life (go to Robert Caro’s magisterial, leave-out-nothing initial volume for that), beginning with him already in the Senate as a powerful majority leader (and reliable member of the Southern contingent) who’s considering a run for the Democratic presidential nomination in 1960, though he assures Robert Kennedy (Michael Stahl-David) that he’s not interested in doing so. Nonetheless he undertakes a losing campaign against Bobby’s brother Jack (Jeffrey Donovan). Along with other matters, that helps to explain why Bobby is apoplectic when Jack offers Lyndon the vice presidential slot for practical electoral-vote reasons.

The team wins, of course, and the second timeframe that takes center stage in Joey Hartstone’s screenplay is Johnson’s unhappy tenure as VP. Shunted to the policy sidelines and treated with undisguised contempt by Bobby and other Kennedy aides (though JFK himself appears somewhat more courteous), Johnson struggles to remain at all relevant. Of course, this section of the film concludes with the 1963 assassination, which thrusts Johnson into the Oval Office, much to the dismay of Bobby.

The third section of the picture concerns how Johnson took up Kennedy’s stalled program and used his congressional know-how to ram it through Congress. The emphasis is on the passage of the Civil Rights Act of 1964, which Johnson embraces with a vigor that shocks old Kennedy hands, leads to a break with Senator Richard Russell of Georgia, his old mentor and friend, and represents, it’s suggested, his final transformation from a regional politician to a figure of national stature.

And that’s where “LBJ” ends. The rest of Johnson’s presidency—his election in his own right, his Great Society programs, and the Vietnam debacle that eventually brought him down—is handled in closing caption cards before the final credits roll. In the end, the film is about a half-decade period in LBJ’s life, from 1959 to 1964, years over which he moved from power to marginalization and then to ever greater power as the result of events over which he had no control.

Though hardly the complete story, however, “LBJ” covers what it chooses to reasonably well, shifting from one timeframe to another to emphasize its points. Johnson’s strained relations with the Kennedys—especially Bobby, who is portrayed as a petulant young man—is nicely conveyed, as is the support Johnson receives from his wife Lady Bird even during the down times. Particularly strong is the depiction of Johnson’s long-time friendship with Russell as one akin to a son’s turning against his father, though one conversation they have, concerning LBJ’s housekeeper, is awfully on-the-nose.

The film’s success in these respects is largely due to casting choices. Jeffrey Donovan is a reasonably convincing JFK, and Stahl-David doesn’t hold back in conveying RFK’s hostility. Jennifer Jason Leigh makes Lady Bird an unfailing prop to her sometimes downhearted husband. And Richard Jenkins is his reliable self as Russell, a man whose segregationist viewpoint is presented as an outmoded perspective that his “pupil” ultimately rejects.

Towering above them all, of course—as Johnson did over everyone while president—is Woody Harrelson. Even with lots of makeup, it has to be said that he doesn’t look all that much like LBJ. But he gets the swagger right, as well as the mixture of coarseness and charisma that could win over Kennedy stalwarts like Kenneth O’Donnell (Michael Mosley) and Ted Sorensen (Brent Bailey) and convince them to stay on the White House staff, even briefly, after the assassination. (Sorensen wrote Johnson’s early presidential speeches, a fact effectively exploited by Hartstone.)

Less successful is the screenplay’s use of Texas Senator Ralph Yarborough (Bill Pullman) as emblematic of the anti-Johnson naysayers who turned into true believers after the new president took up Kennedy’s causes. He first declines to support Johnson’s presidential run, and then agrees to ride in the Dallas motorcade with him only reluctantly, but in the end is shown almost blubbering in his approval as LBJ offers his speech to Congress after the assassination. Yes, it’s a form of dramatic shorthand, but in this case it comes across as obvious and unsubtle.

Not that there’s much subtlety to be found in “LBJ” as a whole. It makes all of its points in a blunt, straightforward fashion, without a great deal of shading. The same might be said of the picture’s technical side. It was mostly shot in Louisiana for tax reasons, but production designer Christopher R. DeMuri makes do fairly well, while Barry Markowitz’s cinematography is unfussy and editor Bob Joyce segues from one timeframe to another and back again, while intercutting the new footage with newsreel material, expertly. Dan Moore’s costume design is fine (the pink outfit worn by Kim Allen’s Jackie Kennedy in the Dallas sequence is right on), and Marc Shaiman’s score is okay, if nothing special.

What prompted Reiner to take up LBJ’s story at this juncture might be a subject of debate. Perhaps it was the desire to show that an ideologically backward, rather vulgar man can be transformed into a real statesman when he assumes the reins of power and achieve great things, as a means of drawing a contrast with somebody else who hasn’t followed a similar pattern. Whatever the motive, however, Reiner’s come up with a fairly standard-issue political docu-drama that’s likely to hold your interest without being especially enlightening or vivid.