"[Y]ou might as well do what you truly feel is right and let the political chips fall where they may"

For Mr. Rubio, a preternaturally gifted politician chastened by a failed White House run, the choice mirrors the broader question facing Republicans on Capitol Hill: Is the price of defying Mr. Trump — who can sink fortunes 140 Twitter characters at a time — worth paying to serve as a critical check on his expansive powers?

“On most major issues you are never going to make everyone happy,” Mr. Rubio said in an email Monday evening, when asked how the experience of running for president had affected his view of this job. “So you might as well do what you truly feel is right and let the political chips fall where they may.”…

Mr. Rubio, who was criticized for appearing overly scripted at times during his presidential campaign, is one of a handful of former Republican candidates working to find his way in the Trump era.

Senator Ted Cruz, Republican of Texas, once Mr. Trump’s most blistering rival, has more recently positioned himself as an eager cheerleader, lauding the president-elect’s nominations with characteristic showmanship.