“On the one hand, he’s one of the most brilliant marketers I’ve ever seen,” Mr. Gingrich said. “And on the other hand, for a while there, he was undercutting himself.”

He added: “I suspect if he had not done that, he’d be ahead by 10 or 15 points right now.”

Talk of rigging the vote rises again.

The chairman of the Nevada Republican Party, Michael McDonald, complained on Saturday night that some polls were being kept open longer than they should have been in Clark County so that “a certain group” could vote.

On Sunday morning, Kellyanne Conway, Mr. Trump’s campaign manager, echoed that concern in an interview with CNN in which she suggested that “special favors” were being done for Democratic voters.

“It’s concerning when you hear reports about special favors and perhaps special rules for Democratic voters,” Ms. Conway said, offering no evidence of a different set of rules. “We already know that their presidential nominee has special rules for her.”

Mr. Trump has for months complained of a rigged system and has said that if he loses the election and there are reports of problems at the polls he might challenge the result.