Washington (AFP) - Republican frontrunner Donald Trump pushed back Sunday against party leaders reportedly looking to block his path to the presidential nomination, saying they were "kidding themselves," as rival Ted Cruz surged in polls.

The push to stop Trump comes as the billionaire real estate tycoon finds himself at the center of a firestorm over his call to ban Muslims from entering the United States.

The Washington Post reported on Thursday that Republican powerbrokers argued at a recent dinner that the party should plan to coalesce around an alternative at the nominating convention if Trump storms through the primaries.

"I think they're making a big mistake. I think I'm the one to beat Hillary," Trump told Fox News Sunday, referring to the Democratic frontrunner Hillary Clinton.

His message to the Republican establishment: "I'm sorry I did this to you, but you've got to get used to it. It's one of the problems in life."

A new NBC/Wall Street Journal poll shows Trump in the lead with 27 percent among Republicans nationally, and other polls give him similar leads in many state contests for the party's presidential nomination.

But the NBC poll also showed that Cruz, a conservative senator who has been careful not to publicly criticize Trump, has surged into second place nationally with 22 percent.

And a Des Moines Register poll out late Saturday said Cruz was leading by 10 points among Republicans in Iowa, site of the first nomination contest February 1.

- 'Cruz-mentum' -

"It's Cruz-mentum. Ted Cruz is crushing it in Iowa," Jennifer Jackson of the Des Moines Register said in a video on the paper's website.

Cruz's 31 percent showing in Iowa versus Trump's 21 percent followed a December 7 Monmouth University poll that also put the Texas senator in the lead in the state.

Cruz has surged as retired neurosurgeon Ben Carson has faded in Iowa, a rise and fall attributed to renewed focus on security issues in the wake of the December 2 attack by a Muslim couple that left 14 dead in California.

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Carson polled fourth in the NBC/Wall Street Journal poll at 11 percent, and third in Iowa at 13 percent in the Des Moines Register poll. Meanwhile, Florida Senator Marco Rubio was third in the national poll with 15 percent and fourth in Iowa with 10 percent.

Trump's response to the Cruz challenge was that the Texas senator lacked the temperament and judgment to be president.

"The way he's dealt with the Senate, where he goes in frankly like a bit of a maniac. You never get things done that way," he said.

"You can't walk into the Senate and scream and call people liars and not be able to cajole and get along with people. He'll never get anything done. That's the problem with Ted," he said.

Questions about Trump's own temperament and suitability to be president have been fodder for debate since he called Monday for a "complete and total" ban on Muslims entering the United States.

The remarks were roundly denounced by Republican leaders as well as the White House, and drew expressions of outrage from around the world.

- Kerry sees 'huge downside' -

Secretary of State John Kerry said Sunday that Trump's anti-Muslim remarks "endanger national security" and that his proposed ban amounted to "a very dangerous foreign policy" that would help jihadist recruiters.

"I think it's got a huge downside in terms of American foreign policy and I hear this from foreign ministers and others as I travel and engage with people in various countries," Kerry said on CBS News' "Face the Nation."

But Trump defended the ban in his appearances on the Sunday talks shows, insisting Muslims should be kept from entering the United States "until we get our hands around this problem."

"There's a sickness. They're sick people. There's a sickness going on. There's a group of people who are very sick. We have to figure out the answer. The Muslims can help us figure out the answer," he said on Fox News Sunday.

An NBC/Wall Street Journal poll earlier this week found that 57 percent of Americans oppose the idea of a ban on Muslims.

On Tuesday, Republican presidential candidates will gather in Las Vegas for their fifth debate leading up to the 2016 presidential election.

Trump, Cruz, Carson and Rubio will be joined by former Florida governor Jeb Bush, businesswoman Carly Fiorina, New Jersey Governor Chris Christie, Ohio Governor John Kasich and Kentucky Senator Rand Paul, CNN announced Sunday.

In order to appear in the debate candidates had to have an average of at least 3.5 percent nationally, four percent in Iowa or four percent in New Hampshire in polls conducted between October 29 and December 13, CNN said.

Meanwhile, former Arkansas governor Mike Huckabee, former Pennsylvania senator Rick Santorum, South Carolina Senator Lindsey Graham and former New York governor George Pataki will appear beforehand in an undercard debate.