Stop the bus, I want to get off.

Other conservatives said that Ms. Palin serves as a particularly effective shield against Senator Ted Cruz, who is battling Mr. Trump for the lead in Iowa polls by courting the state’s evangelical voters.

“Palin’s brand among evangelicals is as gold as the faucets in Trump tower,” said Ralph Reed, the chairman of the Faith and Freedom Coalition.

“Endorsements alone don’t guarantee victory, but Palin’s embrace of Trump may turn the fight over the evangelical vote into a war for the soul of the party,” he said.