Iowa Republican Polls 2015: Is Donald Trump losing support? New survey shows Ted Cruz has taken lead in state poll

If caucuses were held today, Texas Sen. Ted Cruz would beat Donald Trump by a five-percent margin, according a Monmouth University poll of Iowa GOPers released Monday.

The survey of 425 likely Republican voters found that 24 percent support Cruz, compared to 19 percent for Trump; the real estate magnate sits just two percentage points ahead of Florida Sen. Marco Rubio.

Former neurosurgeon Ben Carson, who led by a 14-point margin over Trump in the same poll a month ago, has dropped into fourth place. His favorability rating fell from 84 percent to 64 in that span.

"This marks the first time Ted Cruz has held a lead in any of the crucial early states. As Ben Carson's stock has fallen, Cruz has been able to corral most of those voters," said Patrick Murray, pollster and director of the Monmouth survey. "Congressman King's endorsement may not be the primary reason for this swing, but it certainly put a stamp on the Cruz surge in Iowa."

If the most recent survey indicates anything it's that the Republican Party still doesn't have a clear nominee. Only 20 percent of responded said they've locked in on who they will vote for, and 49 percent said they have a strong preference. Nearly 1-in-5 said Iowa Rep. Steve King's endorsement of Cruz swayed their decision.

The survey was taken between Dec. 3-6, the days following a mass shooting in San Bernardino left 14 people dead and another 21 injured. Republican front-runners have taken the opportunity to flex their foreign policy while denouncing President Obama's handling of the attack.

National security is the most important issue among those surveyed by a 29-to-18 percent margin over government spending concerns.

Cruz and Rubio garnered the most support among Republicans who regularly cast GOP primary ballots, gaining 25 and 21 percent of the votes in this group, respectively. Trump still has 60 percent of the overall vote, but pollsters believe he won't have the same level of support come next November.

"Trump will need a huge organizational effort to get independent voters to show up in a contest where they have historically participated in small numbers," Murray said. "Without this dynamic, the underlying fundamentals appear to favor Cruz and Rubio."