Here’s some welcome news about The Oath, Ike Barinholtz’s tense and shouty comedy about a family trying to get through Thanksgiving as their not-quite-ours America boils over in rage. While watching the film, I not only laughed a lot and gasped oh, shit! in the right places. I somehow never once found myself tempted to sneak a peek at my phone to check in on developments in our real American hellscape. That’s a triumph.

That impulse — to continually stoke our fury with Twitter takes, cable news shouters and breaking news updates — gets lanced throughout The Oath, which writer-director-star Barinholtz has set in a now just as fevered as ours. A megalomaniacal president supported by a fervent right wing has given Americans one year to sign a loyalty pledge, promising that the only punishment for not doing so is the loss of some perks, like a tax credit. That established, Barinholtz cuts to the week before Thanksgiving, just days before the sign-up deadline.

The TV chatters about violent protests, missing citizens and CPUs — in this case, the Department of Homeland Security’s “Citizen Protection Unit,” rumored to be investigating holdouts. Barinholtz plays incredulous lefty Chris, husband to Tiffany Haddish’s more pragmatic Kai, and we see them take in the news in ways familiar to most of us today: He shouts back, cursing at commentators he doesn’t agree with, cheering on those with whom he’s ideologically aligned. She looks shaken by it all but plows ahead with life, her focus not on taking personally each latest outrage but on maintaining a serene existence for their daughter.

Yes, this is a movie where that volcanic comic Tiffany Haddish plays the calm one. That lends a slow-burn suspense to the prickly domestic comedy that Barinholtz has mounted in this counter-America. When will she erupt? Chris’ family is coming to visit for Thanksgiving, and his mother (a splendid Nora Dunn) has emailed everyone a firm edict: No politics! That’s impossible, of course, as everywhere the characters go — driving through the neighborhood, eating at a family-style restaurant — they encounter furious dudes screaming at strangers about the oath or whatever else is on their minds. Barinholtz stages none of these flare-ups for laughs, emphasizing the terror of watching everyday people’s brains boil over.

The key joke of the film’s first half is that nobody’s brain boils more quickly than that of Chris, the principled liberal who fancies himself the voice of reason. He’s right about the monotonousness of the world at large, but he’s also a monster himself. He turns ferocious inquisitor at the mildest of eye-rolls from his conservative brother, Pat (Jon Barinholtz), or Pat’s new girlfriend, Abbie (Meredith Hagner), who announces early on that she loves “mixing it up” with “haters” and “losers” online. He insists on checking in on news alerts during a meal, spouting off about the latest horrors while insisting he’s not talking politics — these are current events. Current events, though, like politics, almost immediately lead to an explosion of fuck yous!, accusations of racism and nasty questions about who has and hasn’t signed the oath. Kai will praise a dish to keep the peace, but even she looks tempted to holler once Abbie declares that Chris Rock is racist.

Also arguing for restraint is another pop-culture Vesuvius, Carrie Brownstein of Portlandia and the all-time-great punk combo Sleater-Kinney. (Watch her expectorate the Bush-era S-K classic “Entertain” for a lesson in controlled, constructive anger far beyond anything Chris can manage.) Brownstein plays Alice, Chris and Pat’s lefty sister, and she proves, as she has in sketch comedy, a nimble and appealing actor, finding laughs and depths in a thinly written character.

The fireworks, when they come, aren’t quite spectacular. Barinholtz is too committed to pressure-cooker realism to give his cast killer punchlines. What’s funny, then, are the shrewdly observed performances, the familiar (from life, not movies) family dynamics, the visiting characters’ terrible luck with overcomplicated TV remotes and the agonizing moments where Chris comes thisclose to letting an offense go — and then can’t quite. Two caveats, though: The most raucous scenes sometimes find everyone yelling for longer than is amusing or revealing, and Haddish’s eventual eruption isn’t scripted or shot with the power the performer deserves. Barinholtz has her posed awkwardly in a corner of the kitchen, not letting her command the frame. (That failing is perhaps balanced out by a tearful scene she kills in the climax.)

The film’s final third complicates the satire, ramps up the shouting and feints toward tragedy. Turns out Chris is right, of course, about this oath. A pair of CPU officers (John Cho and Billy Magnussen) arrive at the house, sniffing for an un-American holdout, and all hell breaks loose. This culminates in lots of scenes of panicky shouting as the squabbling family faces a life-or-death situation of some moral murkiness, something like The Purge meets The Ref. It’s outlandish, a little bloody and just gripping enough. But the voice we hear most, too often, is that of Chris — by this point the least interesting in the movie. If it opened up more and let Kai and Alice’s fears and compromises drive more of its story, The Oath might tell us much more about the now it’s skewering.

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