Mr. Romney was a stand-alone political brand in his own right, but his willingness to discharge antipathy for Mr. Trump made him more than just a political comeback story. On the eve of being sworn into the Senate, Mr. Romney published an op-ed in The Washington Post in which he concluded that Mr. Trump had “not risen to the mantle of the office.” This was two years after then-President-elect Trump had engaged Mr. Romney about possibly serving as his secretary of state. Mr. Romney said he most likely would have taken the job if offered, but it was not — and just as well.

“The best personnel decision he made was not choosing me,” Mr. Romney said. “I would not have lasted as long as Rex Tillerson,” he added of the eventual choice “and maybe a little longer than Anthony Scaramucci did,” referring to the White House communications director who lasted less than two weeks in the job…

“I think that Donald Trump thinks a lot more about Mitt Romney than Mitt Romney thinks about Donald Trump,” said Stuart Stevens, a Republican media consultant and chief strategist of Mr. Romney’s 2012 presidential campaign. “Donald Trump is fundamentally an unhappy, angry person. Mitt Romney is fundamentally a happy not angry person.”