Gore Vidal’s funny, searching “The Best Man” won a Tony Award for best play when it debuted in 1960 and for best revival in 2001 and 2012, and this election year’s brilliant production by The Actors Group, which opened Friday, knocked it out of the convention hall.

The setting is a Philadelphia hotel in July 1960 on the eve of the convention to nominate a party’s presidential candidate. The action opens in the suite of front-runner William Russell (a smart, understated David Farmer), a wealthy, liberal, East Coast intellectual who was secretary of state under former President Arthur Hocksteder, a self-described “good ol’ country boy” whose affability and undercutting sharpness are brought to life by Peter Clark in a role that anchors the production.

The heart of the play is the candidate’s estranged wife, Alice, who has returned to stand by his side and whose ironic wit, bitterness and enduring desire for her philandering husband are beautifully realized by Ann Brandman.

Vidal takes the truism “May the best man win” and examines it with an eye that’s both jaded and fresh, ambiguity being no stranger to the author of “Lincoln” and “Myra Breckenridge.” Vidal knows how to write fully fledged, complex characters even when, as here, they’re placed in stereotypical roles.

We first hear the platitude spoken by Sen. Joseph Cantwell, the dirty trickster candidate with the common touch (he put himself through state college), played with power, drive and a full court of Nixonesque expressions by Al Lanier; and by his wife, Mabel, a Southern sparkler richly embodied by Amy K. Sullivan.

The plot at first hinges on Hocksteder’s crucial endorsement, which he is delaying, enjoying the courtship and the last power play of a dying man. Russell needs it to clinch the nomination because, as his press secretary, Dick Jensen (a comically agonized Stu Hirayama), reminds him, he lacks the popular common touch. “No mention of Darwin. Evolution is out of bounds!” Jensen scolds.

“The women like a regular kind of man,” says party chairwoman Mrs. Sue Ellen Gamadge (a bossy, chilling Cecilia Fordham). Joking is frowned on and wife and family are all-important, she says.

As it turns out, it’s Russell’s decision that will ultimately determine the outcome. Faced with a smear campaign based on his psychiatric record, which Cantwell obtained by bribing a nurse, Russell is given the chance to reveal Cantwell’s “degenerate” sexual history, as a witness terms it.

Although it goes against Russell’s moral fiber, Hocksteder and Jensen beg him to fight, using this “ultimate weapon” if he wants to be “king of the castle.” (“Hamlet” is referenced, as are Sen. Joseph McCarthy’s witch hunts.)

In a climactic scene, Russell tells Cantwell he’s a Frankenstein monster, a self-made man composed of pieces of his victims.

The terrific acting by the entire large cast is supported by evocative lighting and sound, dancing to period blues and rock between scenes, costumes drawn to class and the set design of the backroom in which the political dealings unfold: a painted window with a city skyline, walls painted with furnishings in retro pastels and modernist shapes. The political stakes are telegraphed by large floor stencils of a rocket, a satellite, an American flag and an atomic cloud.

But ultimately it’s the human and moral, rather than political, drama that determines the best man.

TAG’s riveting revival of “The Best Man” works simultaneously as a period play and an update whose savvy direction by Kevin Keaveney connects its 56-year-old themes to this year’s presidential race. Creating a sense of immediacy and intimacy that draws the audience in, it erases intervening time and makes Vidal’s acerbic vision gripping and relevant again.