The competition between GOP presidential candidates Donald Trump and Ted Cruz heated up Sunday, with Trump calling Cruz “a bit of a maniac.”

Appearing on “FOX News Sunday,” Trump said the Texas senator was not qualified to be president because he doesn’t have the right temperament and judgement to get things done.

“Look at the way he’s dealt with the Senate, where he goes in there like a — you know, frankly like a little bit of a maniac,” Trump 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.”

RELATED: Cruz catapults to top in new Iowa poll, leapfrogging Trump

Cruz has a reputation of being critical of his Republican colleagues in the Senate; in a speech this past summer, he said Republican leader Mitch McConnell was lying to the Senate.

In a new Des Moines Register/Bloomberg Politics poll, Cruz leads with 31% of GOP support in Iowa, and Trump follows behind with 10 points less.

Trump still leads in a new NBC News/Wall Street Journal national poll with 27% of support from Republican primary voters. Cruz follows Trump with 22%, a 12 point increase from the last NBC News/Wall Street Journal poll in October. Meanwhile, Ben Carson dropped 18 points since the last poll, dropping from first to fourth place with 11%.

Cruz reportedly criticized Trump’s judgement at a private fundraiser on Wednesday. The New York Times obtained an audio recording of Trump questioning whether Trump and Ben Carson have the judgement to be commander-in-chief.

“Who am I comfortable having their finger on the button?” Cruz asked. “Now that’s a question of strength, but it’s also a question of judgment. And I think that is a question that is a challenging question for both of them.”

Cruz said he does not think either Trump or Carson will be president, and their supporters will turn to him when their campaigns inevitably end.

The Texas senator also distanced himself from Trump recently when he said he did not agree with the business mogul’s call for a ban of all Muslims entering the United States, which Trump continued to defend on Sunday.