“Not everybody is going to follow just because we say this is what we suggest you do,” said Bob Vander Plaats, a leader of the Christian right in Iowa who is a national co-chairman of the Cruz campaign.

He expressed frustration that so-called values voters were giving Mr. Trump a pass on issues about his character, such as his mocking of women, as well as his conservative credentials. Mr. Vander Plaats suggested that they were “either hypocritical or uninformed or maybe not interested.”

“It’s not just three marriages,” he said, listing what he called Mr. Trump’s breaks from conservatism. They included donating to Democrats in the past and once suggesting that his sister, a federal judge who struck down a ban on partial-birth abortions in New Jersey, could make a good Supreme Court justice.

“I understand why you’re ticked off at your government,” Mr. Vander Plaats said of evangelicals who supported Mr. Trump. “But if that’s your one rational reason for casting a vote, then I think you lack discernment, judgment and temperament.”