"Any person in this party that does not support Trump at this point is increasing the chances of Hillary Clinton becoming president and destroying the Constitution," Arizona Rep. Trent Franks told CNN Wednesday. "Therefore they are betraying this party. They are betraying the Constitution."
Franks had endorsed Texas Sen. Ted Cruz in the primary.
The rancor comes after Priebus, the chairman of the Republican National Committee, said Sunday on CBS' "Face the Nation" that if Trump opponents don't "get on board," it's not "going to be that easy for them" to run for office again.
The remark appeared to be directed at former presidential candidates like Cruz, Ohio Gov. John Kasich, and former Florida Gov. Jeb Bush, who all have refused to endorse Trump after signing a pledge to do so during the primary campaign.
Priebus' comments prompted pushback, including from top Kasich strategist John Weaver, who retorted that Kasich "will not be bullied by a Kenosha political operative that is unable to stand up for core principles or beliefs."
But House Republicans had Priebus' back. While none discussed explicit penalties for future candidates based on their opposition to Trump, they warned that there would be political consequences.
"Having on your resume that you were all in against the nominee -- (with a) record number of votes won fair and square -- having on your record that you were against the nominee is not a positive for future political aspirations," said Nevada Rep. Mark Amodei.
Several prominent Republicans in addition to the former candidates have publicly said they won't back Trump. On Tuesday, sources said that former President George H.W. Bush had told Kathleen Hartington Kennedy Townsend that he would be voting for Clinton.
Clinton has also been endorsed by Republicans including HP CEO and former California gubernatorial candidate Meg Whitman; a top adviser to Arizona Sen. John McCain, Mark Salter; and former George W. Bush administration Commerce Secretary Carlos Gutierrez.
Former GOP nominee Mitt Romney has also spoken forcefully against Trump, though he has not endorsed Clinton. And current sitting lawmakers -- including Illinois Sen. Mark Kirk, South Carolina Sen. Lindsey Graham and Florida Rep. Carlos Curbelo -- have said they will not vote for the brash real estate mogul. Kirk and Curbelo are both facing reelection.
On Wednesday, Curbelo brushed off the idea that he is hurting his party.
"Every American has to make the best choice for their country," Curbelo told CNN. "Jack Kemp said you serve your party best by serving your country first, that's what I do here every day."
But Curbelo's colleagues maintained he will have to face the voters' reaction to his opposition to the party's standard-bearer.
"There's already some unrest among Republicans that there are some who have chosen not to get behind their nominee, the person they picked," said Pennsylvania Rep. Lou Barletta. "I can sense that as we travel around, and I think that will be lasting."
"I do anticipate there will be some type of reaction to that," said Tennessee Rep. Marsha Blackburn, referring to Priebus' threat.
Trump has been endorsed by the Republican leaders in the House and Senate, but the relationship has been strained. Though they support voting for Trump, both Senate Majority Leader Mitch McConnell and House Speaker Paul Ryan have continued to on occasion criticize him publicly.
The House's No. 2 Republican didn't fully back Priebus' comments on Tuesday, saying threats were not good motivation to come together.
"There's a better way to unite people. I'm not a big believer that punishment unites people," House Majority Leader Kevin McCarthy told reporters. "If Hillary (Clinton) can't unite Republicans, I don't think anything can."