For a famously mild-mannered man whose worst cuss words are G-rated throwbacks like “golly,” Mitt Romney has a way of getting under President Trump’s skin.

This time, the Republican senator from Utah did it by announcing a bit of good news amid the welter of scary developments during the pandemic: He has tested negative for the coronavirus.

“This is really great news! I am so happy I can barely speak,” Trump tweeted Wednesday morning. “He may have been a terrible presidential candidate and an even worse U.S. Senator, but he is a RINO, and I like him a lot!”

Beyond Trump’s sarcasm about the health of the fellow Republican he considers a nemesis, the president succinctly referenced some of his biggest beefs with Romney.

● He has disdain for Romney over losing the presidential election, handing Barack Obama a second term. If there is anyone who is a bigger thorn in the president’s side than Romney, it’s Obama. “He blew it,” Trump once said of Romney’s candidacy.

● Trump remains furious that Romney was the lone Republican senator to vote to convict him on an impeachment count this year, although this was a mild outburst on that subject. Previously, Trump has called Romney “a disgrace” over the vote. Also “a bad guy,” a “jealous, angry person,” a “pompous ass” and a “lowlife.”

●The insult “RINO,” or “Republican In Name Only,” was meant to dismiss one of the president’s few prominent Republican detractors as a Democratic sympathizer.

The comment also underscored a defining aspect of Trump’s presidency, even during a national crisis when he is being called on to unite the nation — he holds a grudge and very rarely forgets any real or perceived slight.

A spokeswoman for Romney said Wednesday that the senator declined to comment on the president’s tweet.

Romney said Tuesday that he plans to remain in quarantine for the 14 days, as recommended by the Centers for Disease Control and Prevention, “as the test does not rule out the onset of symptoms” later on.

Romney announced Sunday that he was entering quarantine because he had been in close contact with Sen. Rand Paul (R-Ky.) in the days before Paul announced a positive test result.

Trump tweeted support for Paul, who was widely criticized for remaining at the Capitol while potentially contagious, but he greeted news of Romney’s quarantine with what sounded like a wisecrack.

“Romney’s in isolation?” Trump said during an exchange with a reporter on Sunday. “Gee, that’s too bad. Go ahead.”

“Do I detect sarcasm there, sir?” the reporter asked.

“No, none whatsoever,” Trump replied.

The bad blood between Trump and Romney dates at least to 2012, when Trump said the election was Republicans’ to lose and then blamed Romney for doing just that. Trump had endorsed Romney after changing his own party registration to Republican.

Romney shrugged off the critique, but his low opinion of Trump seemed to harden.

By March 2016, when Trump’s own long-shot presidential run had become a juggernaut, some moderate Republicans urged Romney to run again. Instead, Romney threw his support to Trump rivals and delivered a damning assessment of Trump’s fitness for office.

“Think of Donald Trump’s personal qualities. The bullying, the greed, the showing off, the misogyny, the absurd third-grade theatrics,” Romney said.

Speaking in his home state of Utah, Romney condemned Trump as crass, bombastic, ill-informed and, perhaps most insulting to the New York real estate mogul, a business failure who “inherited his business, he didn’t create it.”

“And whatever happened to Trump Airlines? How about Trump University? And then there’s Trump Magazine and Trump Vodka and Trump Steaks and Trump Mortgage,” Romney said, listing off several Trump-branded flops. “A business genius he is not.”

Trump dismissed it all as sour grapes from a “loser” and rubbed Romney’s nose in it as more and more Republicans threw in with Trump.

Romney eventually endorsed Trump, and congratulated his victory. Both men suggested all was forgiven when Romney tried out for a job as Trump’s first secretary of state.

Trump’s public show of auditioning and then rejecting Romney seemed to many to be the outsider president-elect delivering the comeuppance he thought Romney the insider deserved.

Nonetheless, Trump warmly endorsed Romney for his 2018 Senate run, marking their second and perhaps final reconciliation. By 2019, Trump was regularly denouncing Romney as a party traitor, telling audiences that Democrats “don’t have a Mitt Romney in their midst.”

Romney had telegraphed his impeachment vote, which he called a matter of conscience.

He invoked his Mormon faith and the Constitution as he called the decision the hardest of his political life.

“The president is guilty of an appalling abuse of public trust,” Romney said Feb. 5 as he announced his vote.

Romney said he knew he would be “vehemently denounced” for the vote, including from Trump himself.

Indeed, Trump has complained about Romney ever since. Speaking to the Conservative Political Action Conference on Feb. 29, Trump held out the senator from Utah as a turncoat.

“The Republicans stuck together, except Romney, of course,” Trump said, egging on a round of boos from the audience. “You know, Romney. Lowlife. Lowlife.”

Romney has now eclipsed the late senator John McCain (R-Ariz.) as the object of an intraparty presidential grudge. Trump considered McCain a heretic for his 2017 vote on health care and insulted the long-serving Republican even as McCain faced death from brain cancer.

Part of what Trump seems to find galling in both men was a reputation for heroism or rectitude that has eluded Trump himself, said professor Claire Finkelstein, director of the University of Pennsylvania Law School’s Center for Ethics and the Rule of Law.

“Mitt Romney has been a vocal spokesman for ethical conduct while in office, but also has been a model of that kind of conduct. It is part of Trump’s attack on values to try and degrade any individual who demonstrates that kind of leadership,” at what Trump sees as his own expense, Finkelstein said.

Trump said admiration for McCain’s service in the Vietnam War was misplaced because McCain had been captured by the North Vietnamese. Trump said he prefers “heroes who don’t get captured.”

He rejected the idea that Romney had acted on religious conviction or moral imperative.

“Every Republican Senator except Romney, many highly religious people, all very smart, voted against the Impeachment Hoax,” he tweeted on Feb. 14.

Trump drew predictable tut-tutting Wednesday, with critics on Twitter calling his treatment of Romney’s test results insensitive and small. Some comments noted that Romney’s wife, Ann Romney, is at greater risk from the virus because she has multiple sclerosis.

“While Mitt Romney is self-quarantined in the middle of a pandemic, Trump hurls public insults at him,” tweeted former federal prosecutor and CNN commentator Renato Mariotti. “That’s not just beneath the office of the presidency. It’s beneath the basic standard for how any of us should treat other human beings.”

Finkelstein said Trump is missing an opportunity to earn the kind of plaudits he seems to resent when applied to Romney.

Trump could “unify the country and engage in a kind of presidential moment” by wishing Romney well.

“He would have had a moment there to unify the country around this crisis and to show his moral leadership in doing so.”