Republican presidential front-runner Donald TrumpDonald TrumpCavuto disputes Fox clip shows Trump opposing Iraq War Curt Schilling says he wants to run for president Trump brags about winning online debate polls MORE says rival Ted CruzTed CruzFunding bill rejected as shutdown nears Cruz: Clinton 'tired' and 'formulaic' during debate The Trail 2016: Fight night MORE is worried the election is slipping away from him.
"He’s very concerned because his poll numbers are going down, and he looks very, very nervous,” Trump told CNN’s Don Lemon on Wednesday evening.
The business mogul questioned whether Cruz would be able to perform as president after angering so many of his congressional colleagues.
“Everybody dislikes him. I mean, he’s a nasty guy that everybody dislikes," Trump said.
"You're going to have to make deals, you’re going to have to get these senators and congressmen and all of these people, you have to cajole them. … You gotta make deals. We can’t always sign executive orders, you can’t do it. That wasn’t the way our founders set up this country."
At times during the interview, Trump became worked up, raising his voice as he reiterated his attacks on Cruz's eligibility to become president.
"He was born in Canada, and he was a citizen of Canada until 15 months ago, and he says he didn’t know that,” he said.
"He’s got a very big problem because he was born in Canada” and there are experts who think that disqualifies him, Trump added.
"This is a huge problem. So how can the Republicans pick somebody with a very substantial chance that he’s not allowed to run for president?"
Pressed on whether he was driving the issue because he thought it would be in Cruz's best interest, Trump said, "I don’t care about him, I care about the country. I care about the country. I also care about the party."
He also denied ever claiming that Cruz is unqualified to be president, saying he just thinks it's an issue that should be cleared up.
"No, because I’m not making an opinion,” Trump said. “I’m not saying he’s right or wrong or that he has the right to do it or not to do it. I'm just saying it’s something that’s going to be — it’s untested. It’s untested. The Supreme Court has not ruled.”