U.S. Republican presidential candidate Ted Cruz speaks at a 2nd Amendment Coalition announcement at CrossRoads Shooting Sports in Johnston, Iowa, on Dec. 4, 2015. (Brian C. Frank/Reuters)

A prominent evangelical leader in Iowa has endorsed Sen. Ted Cruz's presidential campaign as the Texas Republican's campaign continues to gain momentum.

Bob Vander Plaats, head of the conservative group the Family Leader, said Thursday that he will back Cruz. He was joined by the group's vice president Chuck Hurley and board chairman Robert Cramer, after nine of 10 board members voted that Cruz was the best candidate in the field. (A tenth board member did not vote.)

"At the end of the day, we truly believe that Ted Cruz is the most consistent and principled conservative who has the ability to not only win Iowa but I believe to win the (Republican) nomination," Vander Plaats told the Des Moines Register.

The endorsement was expected, but adds to the roster of prominent conservatives now backing Cruz in the nation's first voting state. Rep. Steve King (R-Ia.) endorsed Cruz last month and well-known radio host Steve Deace backed him earlier this year. The endorsements come as Cruz's campaign is gaining momentum in Iowa. According to a Monmouth University poll released this week, Cruz overtook Donald Trump in Iowa, with 24 percent of respondents saying they would back Cruz opposed to 19 percent for Trump.

Vander Plaats endorsed the last two winners of the Iowa caucus: Rick Santorum in 2012 and Mike Huckabee in 2008. Both men are again running for president, and have campaigned heavily in the state, to little notice in the polls. Santorum was the first 2016 candidate to stump in all 99 counties, and Huckabee has visited 81 of them.

"The political calculations of any single organization will not determine the presidency because Iowa voters are very independent minded and will vote their conscience," Huckabee told the Washington Post in a statement. "We continue to believe that Iowa Evangelicals want a President that knows leadership is more than giving speeches, Iowa farmers want a President that supports them and Iowa seniors want a President who will protect Social Security and Medicare, not cut it."

Santorum spokesman Matt Beynon reacted by dismissing the impact of the personal endorsements, noting that the Family Leader itself would remain neutral. "Senator Santorum learned four years ago that endorsements do not matter in Iowa," he said. "When he surged in mid-December 2011, no prominent groups were standing by Senator Santorum's side."

But Vander Plaats had been at Santorum's side, endorsing him just two weeks before the January 3, 2012 caucuses. Cruz has been trying to coalesce the conservative and evangelical votes in the state and nationwide, in part by pushing aside Santorum and Huckabee. In Iowa, these endorsements could help. The Texas Republican, in the past few weeks, has been working overtime to court the evangelical vote with swings through South Carolina, where he attended a church service and held a religious liberty rally, and Iowa.

[Read: At the center of the Cruz strategy: A play for Christian voters]

One Republican involved in Iowa politics suggested that the clues were there last month, at a donor reception before the Family Leader's Presidential Family Forum. Only four candidates -- Cruz, former Pennsylvania senator Rick Santorum, Sen. Marco Rubio and former Arkansas governor Mike Huckabee -- had beaten a snowstorm to make it there.

But not all candidates were getting the same response. As the Republican made the rounds, he heard a succession of Southern twangs that didn't sound native to Des Moines. Donors who'd ponied up for the event had come from Houston, from Dallas, from Plano -- and all were loyal to their fellow Texan, Ted Cruz.

Santorum and Huckabee had the most to lose from Vander Plaats's move, but the endorsement also added to a run of bad news for Ben Carson. The first-time candidate has seen an autumn polling surge subside in the wakes of media scrutiny and the heightened role of terrorism in the campaign. Evangelical voters, who had crowded his events all year, seemed to be moving toward Cruz even before the Family Leader's decision. Barry Bennett, Carson's campaign manager, said that the candidate could shrug it off.

"We're not terribly surprised by it,"  Bennett said. "Our campaign has been a lot more grass-roots focused than leadership focused. This endorsement's something we wish would have had, but don't think it's going to be determinative. I don't feel sore about it all."

Speaking to reporters after a town hall and speech focused on veterans issues in West Des Moines on Thursday morning, Rubio was asked what his reaction would be if Cruz wins the endorsement of Vander Plaats.

"We're not going to drop out of the race," he said. "We're going to continue to work hard. We would like to have the support of many people as possible," he added. Vander Plaats is someone Rubio has "respect" for, he said.

Sean Sullivan in West Des Moines contributed to this report.