Chris Christie, the former governor of New Jersey, has traveled the world in his quest to stop Donald J. Trump’s march to the Republican nomination. In New Hampshire living rooms as well as the charred homes of Israeli families killed by Hamas, he has assailed the former president as being unfit to lead, antidemocratic and an aspiring dictator.

But now, six months into Mr. Christie’s presidential primary bid, Republicans who share his goal of defeating Mr. Trump are suggesting an entirely different approach for the long-shot candidate.

Quitting.

Republican donors, strategists and pundits are publicly pressuring Mr. Christie to follow the lead of Tim Scott and Mike Pence and formally end his campaign. Many would like him to throw his support behind Nikki Haley, the former South Carolina governor who has risen in the polls in early-voting states in recent weeks.

The focus on Mr. Christie’s bid reflects the anxiety that has consumed anti-Trump Republicans as the race moves into the final weeks before the Iowa caucuses on Jan. 15. Despite three debates, tens of millions of dollars and many months of campaigning, none of the six candidates still challenging Mr. Trump have made much of a dent in his double-digit lead. And they are rapidly running out of time.