Republican presidential front-runner Donald Trump has slammed Senator Ted Cruz as a “maniac” who is unqualified to be president of the United States.
"I don't think he's qualified to be president," Trump said on "Fox News Sunday."
"Look at the way he's dealt with the Senate, where he goes in there like — you know, frankly like a little bit of a maniac. You're never going to get things done that way," he said of the Texas senator.
"You can't walk into the Senate, and scream, and call people liars, and not be able to cajole and get along with people," he said. "He'll never get anything done. And that's the problem with Ted."
The billionaire businessman made the comments less than a week after Cruz told a fundraiser crowd that he was not sure if Trump had the right temperament to be president.
Trump, whose campaign has been marked by controversy from the start, sparked a firestorm last week by calling for a “total and complete” ban on Muslims entering the United States.
Cruz has displaced Trump as the front-runner in some Iowa polls, putting him in prime position to win the first-in-the-nation GOP caucus on February 1.
In a poll released on Saturday night by Bloomberg and the Des Moines Register, Cruz was favored by 31 percent of likely Republican caucus-goers, while Trump stood at 21 percent.
The survey represented a 21-percent jump for Cruz in two months since the last Register poll.
Sen. Cruz has also surged into second place behind Trump in a new national NBC News/Wall Street Journal poll.
Trump leads the GOP field with 27 percent support among Republican primary voters and Cruz is five points behind at 22 percent.
Florida Senator Marco Rubio, a favorite of the GOP establishment, is the first choice of 15 percent of Republican voters in the national poll.
Former neurosurgeon Ben Carson, who was ahead in the last poll, has dropped 18 points to fourth place at 11 percent.