Getting along with your family is hard enough without bringing politics into the equation. But just try getting through Thanksgiving dinner without eventually broaching an issue drawing the ire of at least one of your relatives, especially in these particularly volatile times. One minute you’re breaking bread; the next, breaking jaws. That’s the timely premise of “The Oath,” a dark comedy that avails itself more conservative than liberal when it comes to laughs.

Yet, I can’t say I didn’t grin while bearing it. Ike Barinholtz, the comedian who wrote, directs and stars in it, is actually onto something with his skewering of how we let what we see and hear on cable news and talk radio erode all rationality when it comes to the body politic. Are we right to judge a person merely by how he or she votes, if they even vote at all? Barinholtz seems to think so, and spends 90 occasionally unpleasant minutes driving it home to the point of exhaustion.

Like all great debates, “The Oath” starts off civil and respectful, as Mom (Tiffany Haddish), Dad (Barinholtz), Grandpa (Chris Ellis), Grandma (Nora Dunn), Uncle Patrick (Barinholtz’s real-life brother, Jon) and his new girlfriend (Meredith Hagner), Abbie, join Aunt Alice (Carrie Brownstein) and her dysentery-afflicted husband (Jay Duplass) for a hopefully cordial Thanksgiving dinner amid the backdrop of a massive, violent revolution overtaking the streets of America.

The cause of the uprising is a Trump-like president demanding every citizen sign a “loyalty” oath pledging their devotion to him and the country. The deadline to register is Black Friday, natch. Much to the deep disappointment of Barinholtz’s Chris, most of his family has already acquiesced, something he and his wife, Haddish’s Kai, have proudly refused to bend. So let the bickering begin, particularly between Chris and Patrick, who like his girlfriend, Abbie, is a staunch Republican. And, can you believe it; they think Chris Rock is more racist than funny, which our Chris interprets as a declaration of war. Besides, as Chris points out, Rock is best friends with Adam Sandler and Jerry Seinfeld; so how can he be racist?

Similar, mildly humorous flare-ups solidly fill the first 45 minutes or so. Then after a major blow-up sends Chris out to his Prius (would he drive anything else?) to finish his turkey dinner, a pair of agents (John Cho and Billy Magnussen) from the Citizen Protection Unit, “a division of Homeland Security,” appear at the door. Turns out a member of Chris’ family has reported him disloyal to the president, thus sparking a need for the agents to question him about his refusal to sign the Oath.

It’s here where the movie undergoes a jarring shift in tone, eliciting more cringes than laughs, as violence begets ever-more unsettling brutality. Did Barinholtz really think we’d find beatings, knifings, tasings, and gunshots uproarious? OK, I laughed — but only a couple times, and I hated myself afterward. Most of those rare moments of joviality arrive courtesy of Magnussen’s Mason, a gung-ho American who believes any form of dissonance is punishable by death. He’s the bad cop to Cho’s good cop, Peter, or as Chris’ clueless dad calls him, “the Chinese guy.”

The ensuing standoff between the G-men and Chris’ family fills the film’s rocky back nine, and it only grows more tedious and obnoxious as it drags along. You start to get bored. Then you start thinking about all the holes in Barinholtz’s script. Like: What happened to Chris and Kai’s adorable daughter after the second act?; where are Kai’s family members; why is it that Alice and her husband didn’t bring their two kids with them to Uncle Chris’ house?; and, does Barinholtz actually expect us to swallow a ridiculous, beyond-implausible ending? Not going to happen.

What holds you, even during the film’s clunky finale, are the quality performances from a hugely talented ensemble, with Barinholtz, Haddish, Magnussen and Brownstein emerging as the standouts. All the actors work well together, sharing impeccable timing and potent chemistry. But Barinholtz’s undercooked script allows us only a flash of how excellent “The Oath” could have been with another write-through or three. As is, it’s a clever idea and nothing more; certainly not in the same league as last year’s similarly themed “Dinner with Beatriz.”

There, the mixture of laughs and violence co-existed impressively; here, it emerges clunky and uneven, so much so, I found it near impossible to pledge my full and impassioned allegiance. And like Chris, I’ll gleefully fight to the death defending my obstinance toward something this injurious to my constitution.

“The Oath”

Cast includes Ike Barinholtz, Tiffany Haddish, Jon Barinholtz, Carrie Brownstein, Billy Magnussen, John Cho, Meredith Hagner, Jay Duplass, Chris Ellis and Nora Dunn.

(R for language throughout, violence and some drug use.)

Grade; B-