DES MOINES, Iowa — Sen. Ted Cruz of Texas surged to a 10-point lead in a new poll released Saturday of likely Republican caucusgoers in Iowa, a sign his campaign is gathering momentum and suggesting a long nominating fight is ahead.
Donald Trump, who continues to lead most national polls, was second in the Iowa poll, with 21 percent naming him as their first choice, compared with Cruz's 31 percent.
Ben Carson, after leading an October survey by the same pollster, commissioned by The Des Moines Register and Bloomberg Politics, tumbled to 13 percent. Sen. Marco Rubio of Florida had 10 percent. No other candidate had double-digit support.
The survey, by one of Iowa's most respected pollsters, comes as Trump is increasingly hoping that a win in Iowa, whose caucuses are less than eight weeks away, will be a lightning strike on his way to the nomination.
"If we win Iowa, I think we run the table," Trump said Friday at a rally in Des Moines. He is far ahead in polls of the other early-voting states.
But Cruz's sudden momentum in Iowa complicates Trump's plan. It could set up a protracted primary between Cruz, as the choice of far-right Republicans, Trump as an anti-establishment outsider, and perhaps a third candidate representing the center-right of the party.
Long locked in a mutual nonaggression pact, Cruz and Trump have teetered on the brink of hostilities in recent days.
After studiously avoiding any public attacks on Trump for fear of becoming a target of his derision, Cruz privately told donors this week that Trump had questionable judgment, according to an audio recording of his remarks. The comments came two days after Trump proposed barring Muslims from entering the United States as a way to combat terrorism; Cruz said he disagreed but did not criticize Trump as others have.
In a series of Twitter posts after his "judgment" comments became public, Cruz tried to play down any rift, while Trump moved toward escalation.
Cruz wrote: "The Establishment's only hope: Trump & me in a cage match. Sorry to disappoint — @realDonaldTrump is terrific."
Trump struck a different tone. "Looks like @tedcruz is getting ready to attack," he wrote. "I am leading by so much he must. I hope so, he will fall like all others. Will be easy!"
And in a speech in Des Moines on Friday, Trump criticized Cruz's opposition to federal support for ethanol, an important state industry, and in a more audacious attack, he questioned Cruz's faith.
"And by the way, I do like Ted Cruz," Trump said, "but not a lot of evangelicals come out of Cuba. It's true. Not a lot come out."
Cruz, whose father, Rafael Cruz, emigrated from Cuba and is a fiery evangelical pastor, has succeeded more than any other candidate in enlisting conservative Christian support in Iowa. On Thursday, he won the endorsement of Bob Vander Plaats, a leader of the Christian right in Iowa.
Despite Trump's repeated assertions that he is "doing really well with the evangelicals," his attack on Cruz's faith risks pushing away that large group of politically active voters, who in the past two Republican caucuses played a decisive role in choosing the winner, Mike Huckabee in 2008 and Rick Santorum in 2012.
In a poll released Monday by Monmouth University, Cruz emerged as the top choice of evangelical voters, comfortably ahead of Trump and with about twice the support of Ben Carson, the retired surgeon, who also appeals to social conservatives.
On ethanol, Trump suggested Cruz was hypocritical for opposing federal support for that fuel, a major Iowa industry, while backing tax breaks for oil companies.
"With the ethanol, really, he's got to come a long way because he's right now for the oil," Trump said, echoing an ethanol group that has tried to make the issue central to the campaign. "But I understand: Oil pays him a lot of money; he's got to be for oil, right?"
It is unclear whether enough Iowans rank the issue highly enough to make a difference. Cruz has won the endorsement of Rep. Steve King of Iowa, an ethanol champion.
Trump also sought Friday to undermine the credibility of The Register poll even before it appeared, singling out the newspaper, the most influential in Iowa, during a customary interlude in which he attacks the news media.
"I'll tell you, you have one of the most dishonest right here in your backyard: The Des Moines Register is the worst," he said to cheers and applause. "Some reporter named Jacobs, she is the worst," he said, referring to The Register's lead political reporter, Jennifer Jacobs.
He accused the paper's polling, which has consistently been among the most accurate in surveying Iowa voters, of bias against him.
Trump has been on the warpath against The Register since the paper's editorial board called on him to quit the race in July because "he has polluted the political waters." The editorial board, which endorsed Mitt Romney before the 2012 caucuses, has not yet announced its preference for 2016.
On Friday, Trump promised to campaign aggressively in Iowa, returning almost full time to the state in the three weeks before the Feb. 1 caucuses.
"If I win Iowa, I think it's over," he repeated.
Trump's fear seems to be that if no candidate enters the Republican convention in July with enough delegates to win, it would trigger a stop-Trump movement with lower-performing candidates throwing their support to one of his competitors.
He warned Friday of "bloodsucker politicians" controlling the convention and also repeated his threat to run as an independent.
"You'll know in a month or two whether the establishment is treating me favorably," he said.