“There’s this desire, verging on panic, to consolidate the field,” said Senator Lindsey Graham of South Carolina, a former supporter of Mr. Bush. “But I don’t see any movement at all.” Mr. Rubio’s advisers were also thwarted in their efforts to secure an endorsement from Mr. Romney, whom they lobbied strenuously after the Feb. 20 South Carolina primary. Mr. Romney had been eager to tilt the race, and even called Mr. Christie after he ended his campaign to vent about Mr. Trump and say he must be stopped. On the night of the primary, Mr. Romney was close to endorsing...