As Ben Carson solidifies his new position as the Republican presidential frontrunner in Iowa, Donald Trump is pledging to "work a little bit harder."

In an interview with CNN's Jake Tapper set to air Sunday at 12 p.m. ET, Trump admits he was shocked to see Carson, a retired neurosurgeon, move past him in the earliest voting state.

Two separate polls this week found Carson surging to first place in Iowa with 28 percent support while Trump lagged behind at 20 percent and 19 percent. A third survey of likely Republican caucus-goers in Iowa conducted by the Believe Again PAC also found Carson leading Trump 28-20 percent.

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"I was really surprised to see it because, you know, I was just in Iowa three days ago and we drew a packed crowd," the real estate mogul told Tapper.

"I've done really well with the evangelicals and with the Tea Party and everything and I just don't understand the number, but I accept the number," he added. "It means I have to work a little bit harder in Iowa."

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