On Sunday, one influential conservative went so far as to say he could not be sure of Romney's safety at a major right-wing gathering, alarming some of the Utah senator's defenders and - in some critics' eyes - crossing a line from outrage to threat.
Matt Schlapp, chairman of the Conservative Political Action Conference, made the controversial comments Sunday as he explained why Romney would be excluded from this year's event, set for Feb. 26-29 in nearby National Harbor, Maryland. Schlapp announced last month via tweet that the senator was "formally NOT invited," as Romney took heat for breaking from staunch Republican support of the president to call for witnesses in Trump's impeachment trial.
"We won't credential him as a conservative," Schlapp told Greta Van Susteren on "Full Court Press." "I suppose if he wants to come as a nonconservative and debate an issue with us, maybe in the future we would have him come."
He added, "This year, I would actually be afraid for his physical safety, people are so mad at him."
The suggestion of potential violence stuck out even in an onslaught of criticism of Romney, drawing some rebukes.
"Closer and closer to saying the quiet part loud," tweeted Rick Wilson, a prominent "Never Trump" Republican and media consultant.
"It's hard to believe that we have stooped this low," Romney's Senate colleague Joe Manchin, D-W.Va., said on CNN, after calling the Utah politician as "honorable" a person as he had ever met. Manchin, a political moderate, has also been a target of Trump's ire and name-calling ("Joe Munchkin") after defying significant pressure to vote for acquitting the president last week.
Others just marveled.
"This is remarkable," wrote Atlantic writer McKay Coppins, who last fall profiled Romney as "an outspoken dissident in Trump's Republican Party" who found his voice "just in time for the president's impeachment trial."
Schlapp has denied any threatening intent in his Sunday comments, tweeting that he has "no beef [with Romney's] family" and hopes "they have happy healthy lives away from politics." Responding to one man's accusation that he runs a "mob," Schlapp said he has taken his "little girls" and 80-year-old mom to CPAC without any problem.
"I wish Gov Romney no harm I just want him to find a new hobby away from destroying GOP momentum," the conference head said.
Speaking to Van Susteren on Sunday, Schlapp called Romney a "use 'em and lose 'em kind of guy," accusing him of cozying up to Trump when he needed the president's endorsement for reelection and then diverging once he had his Senate seat.
He alleged a similar relationship between Romney and CPAC, which bills itself as "the largest gathering of grassroots conservatives on the planet."
"He said he was going to be an extreme conservative, that he was the most conservative guy in the world, and when he came to CPAC, after 2012, he doesn't want to have anything to do with us," Schlapp said.
Romney did return to CPAC in 2013 to give a speech.
"As someone who just lost the last election, I'm probably not the best person to chart the course for the next election," he said before laying out his advice to fellow conservatives.
Romney has not attended the annual event since, and his plans for this year were not clear. A representative for Romney declined to comment Monday, and CPAC did not immediately respond to an inquiry from The Washington Post.
Scheduled for the end of February, CPAC boasts a speaker lineup of lawmakers, media personalities and right-wing celebrities. Its website touts prominent names ranging from "Godfather of #Brexit" Nigel Farage to Ronna McDaniel, chairwoman of the Republican National Committee.
McDaniel took a less combative tone last week when she broke with Romney, her uncle, on the issue of impeachment.
"This is not the first time I have disagreed with Mitt, and I imagine it will not be the last," McDaniel tweeted.
But elsewhere in the GOP, the reaction to Romney's vote - the first instance of a senator voting to remove his own party's president from office - has been livid.
The Republican National Committee blasted the lawmaker in an email last Wednesday under the subject line "Mitt Romney turns his back on Utah," while Donald Trump Jr. declared on Twitter: "He's now officially a member of the resistance & should be expelled" from the GOP.
Explaining his decision on the Senate floor, Romney anticipated a fierce backlash but framed his vote as a "duty."
"I will tell my children and their children that I did my duty to the best of my ability, believing that my country expected it of me," he said.