Story highlights Donald Trump has been in second place in recent polls to retired neurosurgeon Ben Carson

Trump attacked Carson in a Tuesday morning interview

Four polls in Iowa and at least one national poll have shown Trump in second place

Washington (CNN) Donald Trump said he doesn't understand his recent drop in polls, but he continued his attacks on Ben Carson, who has knocked him from the top spot in Iowa and -- in at least one survey -- nationwide among Republicans.

"I don't get it," Trump said on MSNBC's "Morning Joe" on Tuesday. "I'm going there (to Iowa) actually today and I have tremendous crowds and I have tremendous love in the room and, you know, we seem to have hit a chord. But some of these polls coming out, I don't quite get it. "

Trump kept up his attacks on Carson, who is beating him handily in a series of four polls from Iowa and as of Tuesday morning overtook the top spot nationwide in the latest CBS News/New York Times poll.

"You know Ben wants to knock out Medicare. I heard that over the weekend, he wants to abolish Medicare. And I think, you know, abolishing Medicare. I don't think you're going to get away with that one. And it's actually a program that's worked," Trump said.