Cruz is now the number one choice for 31 percent of likely Iowa GOP caucus goers, up 21 points from the last time the poll was taken. This is the biggest leap in five caucus cycles, the newspaper's records show.
Trump trails Cruz at 21 percent, with Carson at 13 percent, Marco Rubio at 10 percent and Jeb Bush at 6 percent. Carson faced the biggest decline, losing 15 percent and falling from front-runner to third place.
One factor for Cruz's rise could be the support of the more conservative wing of the party. This poll shows him gaining the support of 45 percent of evangelical conservatives and 39 percent of tea party conservatives. Maintaining the lead among evangelicals is a key to winning the Feb. 1 caucus in Iowa because about half of caucus goers identify as evangelicals.
In considering the likeability factor, Cruz is also doing well. Cruz is now 73 percent favorable, which is up 12 points from October. This is the highest out of any of the candidates - Trump is 53 percent favorable.
The poll comes days after two other polls showed conflicting Iowa results: a CNN poll showed Trump maintaining the lead in Iowa, and a Monmouth poll showed Cruz in the lead.
Trump, who called the Register "the worst" at a rally in Des Moines Friday night and predicted that the poll would show him disappearing, was quick to bash the results on Twitter.
Cruz has spent 13 days been in Iowa since the beginning of October and had over 40 events. He has also committed to barnstorming the state - his plan is to hit all 99 counties before the caucus.
"I do not think that this is by any means strange," said Craig Robinson of The Iowa Republican. He has seen the Cruz momentum grow in the state but questions Cruz's ability to maintain this high water mark. "So much of politics is positive momentum. Maybe this is too high of a peak too soon. You have to maintain this for 50 days, which is the tough part."
The poll also showed a remaining affinity for the "outsider" candidate, which could benefit Trump. Thirty-nine percent would prefer a government outsider while 30 percent would prefer a senator and 19 percent a governor.
Because national security and terrorism are the most important issues for Iowa GOP caucus goers -- as shown in a recent Iowa poll from Americans for Peace, Prosperity and Security -- it is noteworthy that 35 percent of the respondents to Saturday's poll said that Trump was the best candidate to combat Islamic terrorism. Cruz was just behind with 33 percent and Rubio with 13 percent.
Bush and Rubio did not move much in Saturday's poll. Bush, who has never broken double digits in this poll, is at 6 percent, but his unfavorables climbed up to 54 percent. Rubio, on the other hand, maintains a high favorability rating of 70 percent.
Still, only 33 percent of respondents said their mind is "made up."
"I do not expect anybody who is at the top right now to stay at the top," said pollster Ann Selzer, noting that there are many past candidates who have fallen in the last poll.
She also said that she "has never seen leaps of this magnitude," referring to Cruz, and that Cruz may be "cashing in" on the recent endorsements from Rep. Steve King, R-Iowa, and Bob Vander Plaats, a conservative leader in Iowa.
The Des Moines Register/Bloomberg Politics poll of 400 likely Republican caucus goers was conducted Dec. 7-10 by Selzer & Co. of Des Moines. The margin of error is plus or minus 4.9 percentage points.
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