Frank Cannon, president of American Principles in Action, said he is surprised that Mr. Cruz would make such a public statement.

“I think he senses the certain beginning of a weakness, or at least a stop in the Trump rise, and as the potential for a Trump collapse — or at least a retrenchment of the Trump vote — increases, he wants to be able to pick that up,” Mr. Cannon said. “He is making the calculation that he had to be out there in front and make an active bid for that. I am a little surprised by the timing, but I think the strategy has been clear since the beginning.”

Mr. Tyler downplayed the remarks, suggesting the media response to the comments were overblown.

“It would be news if he said Trump is going to be the nominee,” he said, adding that Mr. Cruz wants to win over voters who are lined up behind various candidates. “Our quest to win over Trump voters is not unique to Trump, but he does have the most voters” based on polls.