Mr. Rubio’s campaign, once hopeful that Florida would be the final stop on his road to the nomination, has gone from fighting for its life to just getting through the day.

“If I never hold elective office again, I’m comfortable with that,” Mr. Rubio said at a news conference here on Friday, answering yet another question that was some variation of “Why don’t you just throw in the towel?” or “Will you try to run again next time?”

Mostly gone is the sunny optimism of those at his side throughout his deflating and exasperating run. They acknowledge that the end is probably near, and say they just want it to be as painless as possible…

His friends and longest-serving aides say that dropping out would be an act of betrayal to Floridians who have cast mail-in ballots for Mr. Rubio already, rendering their votes worthless.

And they contend that Mr. Rubio is doing his party a favor, by trying to deprive Mr. Trump of the delegates necessary to clinch the nomination — a sacrifice, they say, that will someday be repaid by grateful Republicans. To drop out now, they argue, would be to surrender the state’s 99 delegates to Mr. Trump.