WASHINGTON - Republican presidential front-runner Donald Trump had a new target on Sunday, calling fellow White House contender Ted Cruz a "a little bit of a maniac" as the US senator surpassed him in an Iowa presidential poll.Cruz's dogged pursuit of conservative Iowa voters has paid off in the form of a 10-point lead over Trump in the state with one of the earliest presidential contests.Unlike the other Republicans in the 2016 White House race, the US senator from Texas has embraced Trump and avoided public criticism of the popular candidate.But last week he questioned Trump's judgment at a private fundraiser, according to the New York Times, after the billionaire businessman advocated temporarily banning Muslims from entering the United States.That got Trump's attention."I don't think he is qualified to be president," Trump said on "Fox News Sunday"."I don't think he has the right temperament. I don't think he's got the right judgment. When you look at the way he has dealt with the Senate, where he goes in there like a, you know, frankly, like a little bit of a maniac - You are never going to get things done that way."Trump touted his ability to get along with liberals and conservatives and said that was the hallmark of the "world-class businessman" he is.The incendiary front-runner, whose comments on Muslims drew widespread criticism but may not dent his lead in several national public opinion polls, made a sarcastic reference to Cruz's respectful treatment of him."He's been so nice to me. I mean I could be saying anything and he'd say, I agree I agree." Trump said on CNN's "State of the Union".On the Fox program, he also criticized Cruz for talking about him behind his back.