"My siblings who chose to film ads against me are all liberal Democrats who hate President Trump," Gosar wrote in one of several tweets. "These disgruntled Hillary suppporters [sic] are related by blood to me but like leftists everywhere, they put political ideology before family."
"Stalin would be proud," he added.
Campaign ads featuring six Gosar siblings condemning their brother and endorsing his opponent, David Brill, first went online on Friday. The videos feature six of the 10 Gosar children, who are originally from Wyoming: Tim, Joan, Grace, David, Jennifer, and Gaston.
First reported by Phoenix New Times, the endorsements quickly became a national news story, with political observers calling the ad campaign one of the most jaw-dropping they have ever seen.
One ad for Brill racked up over 868,000 views on YouTube by Saturday afternoon. Brill's Twitter account gained well over 1,000 Twitter followers after the ad campaign went live.
Paul Gosar, a four-term congressman who represents the Fourth Congressional District, noted that all of his siblings live outside Arizona. On Twitter, he called Brill's policies "out of sync with what Arizona wants and the country needs."
"I will not be deterred from fighting for our conservative values regardless of these attacks," Gosar wrote.
In one 60-second ad for Brill entitled "Paul is Not Working for You," at first, there's no mention that the six men and women on camera are related to Gosar – after denouncing the congressman's policies, they state their names, revealing that Gosar is their brother.
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
"He's not listening to you, and he doesn't have your interests at heart," Tim Gosar says in the ad.
In another video shown by the Brill campaign at a fundraiser in Phoenix on Thursday, Gosar's sister Grace says, "It would be difficult to see my brother as anything but a racist." The ad is not yet online.
In an interview with New Times on Friday, David Gosar said that none of the siblings relish speaking out against their brother, but they feel like they have no choice because Gosar has embraced conspiracy theories and fringe politics.
Gosar's speech at a London rally for an extremist anti-Muslim group in July was unacceptable, his brother said. “It’s appalling. It’s disgraceful," David Gosar said.
He regularly tweaks his politician brother on Twitter, calling him "Weasel." A campaign staffer for Brill spied his tweets, which led to a conversation between David Gosar and the campaign, and then a trip to Wyoming to film the ads with the Gosar siblings earlier this month.
David Gosar didn't predict that the ad campaign would spark a national political conversation.
“I don’t really expect it to be much more than a local or perhaps a regional story," he said on Friday, before the ads went viral.
Brill, a Prescott doctor, is very much a long-shot to defeat Gosar.
The Fourth District is a Republican stronghold that includes the cities of northwest Arizona and areas surrounding metro Phoenix. Gosar did not face a Republican primary challenger this year.
Another tweet in response to the ad campaign was less grim than the "Stalin" reference.
"You can't pick your family. We all have crazy aunts and relatives etc and my family is no different," Gosar wrote. "To the six angry Democrat Gosars – see you at Mom and Dad’s house!".