Several senior Republicans, including Mr. Romney, have made direct appeals to Mr. Kasich to gauge his willingness to stand down and allow the party to unify behind another candidate. But Mr. Kasich has told at least one person that his plan is to win the Ohio primary on March 15 and gather the party behind his campaign if Mr. Rubio loses in Florida, his home state, on the same day…

While still hopeful that Mr. Rubio might prevail, Mr. McConnell has begun preparing senators for the prospect of a Trump nomination, assuring them that, if it threatened to harm them in the general election, they could run negative ads about Mr. Trump to create space between him and Republican senators seeking re-election. Mr. McConnell has raised the possibility of treating Mr. Trump’s loss as a given and describing a Republican Senate to voters as a necessary check on a President Hillary Clinton, according to senators at the lunches.

He has reminded colleagues of his own 1996 re-election campaign, when he won comfortably amid President Bill Clinton’s easy re-election. Of Mr. Trump, Mr. McConnell has said, “We’ll drop him like a hot rock,” according to his colleagues…

Mr. Christie had attacked Mr. Rubio contemptuously in New Hampshire, calling him shallow and scripted, and humiliating him in a debate. Nevertheless, Mr. Rubio made a tentative overture to Mr. Christie after his withdrawal from the presidential race. He left the governor a voice mail message, assuring Mr. Christie that he had a bright future in public service, according to people who have heard Mr. Christie’s characterization of the message.

Mr. Christie, 53, took the message as deeply disrespectful and patronizing, questioning why “a 44-year-old” was telling him about his future, said people who described his reaction on the condition of anonymity. Further efforts to connect the two never yielded a direct conversation.