As Trump and Cruz soar, GOP leaders' exasperation grows

Some in the party now concede that it might take until March or beyond for the Republican establishment to coalesce behind an alternative to the current front-runners. And that could be too late to catch either Mr. Trump or Mr. Cruz.

Judd Gregg, a former senator from New Hampshire, said he believed his state would cull the field, but he acknowledged that the primary calendar — and the lineup of conservative Southern states that vote in March — could prolong the race.

Robert F. List, a former Nevada governor, agreed.

The current “circular firing squad against the lower team,” Mr. List said, “is not helpful.”

Many in the party say they believe the assault by Mr. Bush against Mr. Rubio has been particularly damaging.