Arizona Congressman Paul Gosar, a Republican from the party's most conservative wing, is standing for re-election in November.
Fearing for the future, his siblings have thrown their weight behind their choice of candidate in a powerful new TV advert.
The striking part? It's not their brother.
Nope - six of Mr Gosar's siblings have spoken out to endorse his rival, Democrat David Brill.
If that sounds brutal on paper, the execution is even more savage. To maximise its impact, the ad doesn't name the six speakers until the end - they're just presented as normal Arizona folks.
It opens with "Grace, rural physician", declaring, "Paul Gosar the congressman isn't doing anything to support rural America."
"Paul's absolutely not working for his district," says "David, lawyer".
"If he actually cared about people in rural Arizona, I bet he'd be fighting for social security, for better access to healthcare," agrees "Jennifer, medical interpreter".
"He is not listening to you, and he does not have your best interests at heart," "Tim" agrees - before dropping the bombshell line: "My name is Tim Gosar".
So is this a shock move from David, Tim, Jennifer, Gaston, Joan, and Grace?
Local paper the Arizona Republic calls it "brutal, but not unexpected". Mr Gosar made headlines after the violent neo-Nazi rally in Charlottesville, Virginia, in August 2017, by suggesting it was planned by "the Left" to undermine Donald Trump. He then branded Democratic Party donor George Soros a Nazi collaborator in an interview with Vice News.
Horrified, seven of his siblings signed an open letter to the Kingman Daily Miner, stating: "It is extremely upsetting to have to call you out on this, Paul, but you've forced our hand with your deceit and anti-Semitic dog whistle."
Paul Gosar's other controversies include boycotting a 2015 speech to Congress by Pope Francis. He criticised the pontiff's support for climate change, calling it "questionable science" deployed "to guilt people into leftist policies".
He has also defended British far-right activist Tommy Robinson, and attacked "disgusting and depraved" Muslim immigrants at a speech in London in July.
Further anti-Gosar adverts set to air on TV soon include one titled "A family defends its honor," where David Gosar says: "We've got to stand up for our good name, this is not who we are."
"It would be difficult to see my brother as anything but a racist," Grace Gosar says in another, according to the Phoenix New Times.
Representative Gosar responded to the ad campaign in a series of scathing tweets on Saturday.
In it he labelled his siblings as "disgruntled Hillary supporters" and said "see you at Mom and Dad's house!"
My siblings who chose to film ads against me are all liberal Democrats who hate President Trump. These disgruntled Hillary suppporters are related by blood to me but like leftists everywhere, they put political ideology before family. Stalin would be proud. #Az04 #MAGA2018— Paul Gosar (@DrPaulGosar) September 22, 2018
You can’t pick your family. We all have crazy aunts and relatives etc and my family is no different. I hope they find peace in their hearts and let go all the hate.— Paul Gosar (@DrPaulGosar) September 22, 2018
To the six angry Democrat Gosars—see you at Mom and Dad’s house! #AZ04 #MAGA2018
The Republican, who won his district with 71% of the vote in 2016, is still considered likely to keep the seat he has held since 2011.
If there is a bright side for Mr Gosar, it's that he is one of 10 siblings. While seven have denounced him in public, two are keeping their silence so far - which might make Christmas fractionally less awkward.
His mother has also vocally supported his leadership and politics, leading him to quip: "I guess I really am Mom's favourite"
More attack ads: Nuclear war, a 3am phone call, and Trump's decade-old favourite
Paul Gosar is far from the first US politician to be targeted by a critical advert, of course.
So-called "attack ads", in which a candidate lambasts their opponent instead of stressing their own virtues, have been a recognised tactic since the 1960s.
When Democrat Lyndon Johnson was running against Republican Barry Goldwater in the 1964 presidential election, one famous TV ad featured a young girl counting down as she pulled petals off a daisy, then cut to a nuclear explosion.
Johnson's voice boomed over the footage: "These are the stakes. To make a world in which all of God's children can live, or to go into the dark. We must either love each other, or we must die."
Mr Goldwater was never mentioned, but the message was clear - his more aggressive attitude to the Cold War would imperil the public and could lead to nuclear doom. Johnson was the only safe choice. The ad was considered controversial, but highly effective. Johnson won by a landslide.
Decades later, Hillary Clinton deployed a slightly subtler but clearly negative ad against Barack Obama, her rival in the 2008 Democratic presidential primaries. It opened with shots of children fast asleep, and a voiceover saying, "It's 3am and your children are safe and asleep. But there's a phone in the White House, and it's ringing. Something's happening in the world..."
The message urged voters to choose someone who "already knows the world's leaders, knows the military" and is "tested and ready to lead in a dangerous world" to pick up the phone. The implication: Obama lacks the experience to lead.
The future president wasn't above making digs of his own, however.
In June 2016, then presidential candidate Donald Trump dug up an old Obama radio advert criticising Mrs Clinton for making "false attacks" and shared it online. He tweeted: "I rarely agree with President Obama - however he is 100% correct about Crooked Hillary Clinton. Great ad!"
I rarely agree with President Obama- however he is 100% correct about Crooked Hillary Clinton. Great ad!https://t.co/aOvVsZfAW3— Donald J. Trump (@realDonaldTrump) June 10, 2016