"He's done. It's just—he is."

Mr. Gingrich’s spokesman, R.C. Hammond, says Mr. Gingrich’s path to victory relies on Mr. Romney dropping out—a highly unlikely scenario.

“That has the same possibility as a moon colony with enough people to apply for U.S. territory status,” said Curt Anderson, a now-unaligned former adviser to Texas Gov. Rick Perry, in reference to one of Mr. Gingrich’s policy proposals. “He’s done. It’s just—he is.”…

Assuming Mr. Romney doesn’t drop out of the race, Mr. Gingrich could still get yet another look from voters if Mr. Santorum is not able to win Tuesday in Michigan and Arizona, where polls show a tightening race, said Bob Walker, a former congressman and adviser to the Gingrich campaign.

The thinking goes that Mr. Santorum would then demonstrate he can’t beat Mr. Romney in a one-on-one race, weakening his argument as a conservative alternative to the former Massachusetts governor.