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On America’s Election Headquarters tonight, Charles Krauthammer weighed in on GOP frontrunner Donald Trump's prospects for Iowa and beyond.

Krauthammer said that Trump has the most "hardcore" supporters, citing a Des Moines Register poll that showed seven of 10 Trump supporters saying they wouldn't change their minds, which was more than all of the other candidates.

But he said that Trump's problem is that he has a soft appeal beyond those supporters, and that only 7% of caucus-goers have named him as their second choice, while other candidates have received a higher percentage.

"It suggests that whoever can get through Iowa, perhaps New Hampshire, they have room to grow much more than Trump," he said.

Krauthammer said the most striking number in the poll is the favorable-unfavorable, noting that Trump's favorability rating is mostly flat (+3% favorable) compared to other candidates (Rubio +49%; Cruz +37%), who are seen as much more favorable.

"The reason is that the Trump is support is very hardcore, very loyal. Again, can he grow beyond that? If the others get through you could see them collecting the votes of the others who are winnowed out of the field. And that would make it a very tight two-way race or three-way race."

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