For most of the 2016 presidential campaign, New York billionaire Donald Trump and Texas Sen. Ted Cruz have been virtual bosom buddies. That may be changing.

Cruz was caught on tape last week at a private fundraiser questioning Trump’s judgment to be commander in chief. Sunday, Trump fired back.

Appearing on “Fox News Sunday,” Trump said Cruz is “not qualified to be president” and brought up the senator’s reputation for combativeness against his Senate colleagues.

“When you look at the way he’s dealt with the Senate, where he goes in there like a — you know, frankly, like a bit of a maniac,” he said. “You never get things done that way.”

Trump also blasted Cruz for not criticizing him in the open.

“Do you notice he said it behind my back, somebody taped that conversation?” he said. “He said it behind my back … He’ll never get anything done, and that’s the problem with Ted.”

On CNN’s “State of the Union,” Trump disputed Cruz’s assertion that he lacks judgment to be commander in chief.

“My judgment’s great,” Trump said. “I built a multi-, multi-, multibillion-dollar company. Some of the greatest assets in the world … You don’t make that kind of success without judgment.”

Trump said he was against the war in Iraq before conventional wisdom turned against it.

“I would say I have been far better judgment than Ted, and I think I have a really great temperament,” he said. “It’s a strong temperament … I’m more capable. Because, I’ve got much better temperament. Because I actually get along with people much better than he does.”

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Trump railed as new polls show Cruz on the move and largely battling for the same base of voters as Trump. Cruz overtook Trump for the lead in a pair of polls of Republicans in Iowa. A DMR/Bloomberg poll showed Cruz over Trump by 31 percent to 21 percent. And a Fox News survey gave Cruz the edge by 2 percentage points.

Nationally, an NBC/Wall Street Journal poll found Cruz with 22 percent support, just five points behind Trump.

Nationally, an NBC/Wall Street Journal poll found Cruz with 22 percent support, just five points behind Trump.

Trump also took a moment during his Fox appearance to attack Hillary Clinton, responding acerbically to her contention that he is dangerous.

“She is the one that caused all this problem with her stupid policies,” he said. “You look at what she did with Libya, what she did with Syria. Look at Egypt, what happened with Egypt, a total mess. They don’t back — we don’t back any of our allies. You look, she was truly, if not ‘the,’ one of the worst secretary of states in the history of the country. She talks about me being dangerous. She’s killed hundreds of thousands of people with her stupidity.”

Sen. Marco Rubio, the Florida Republican who is third in many GOP polls and has emerged as the Establishment front-runner, lobbed barbs Sunday at both Trump and Cruz.

“The most important thing a president will be is commander in chief,” he said on “Meet the Press” with Chuck Todd. “And that requires having an understanding of the complex issues on foreign policy … I personally believe he continues to struggle to articulate that.”

Rubio praised Trump for touching on issues that concern voters. But he blasted Trump’s recent proposal to temporarily ban Muslims from coming into the United States.

“It’s offensive and outlandish in the sense that, for example, it’s not going to happen, No. 1,” he said. “I think it violates a lot of the things that we think about our country.”

Rubio said Cruz’s record does not match his rhetoric on national security.

“He talks tough on some of these issues … but the only budget he’s ever voted for in his time in the Senate is a budget that cut defense spending, by more than Barack Obama proposes we cut it,” he said. “He voted against the Defense Authorization Act every year that it came up.”

The latest CBS polls indicates that 54 percent of Republican voters support a ban on Muslims entering. Ohio Gov. John Kasich, one of the Trump’s fiercest critics in the GOP primary field, did what politicians often do when confronted by a negative poll — he disputed its accuracy.

“Now let me also say about your polls, you’re polling, like, 400 people out of 325 million,” Kasich said on “Face the Nation” on CBS. “So I see polls all the time. I’ve become more convinced now that the reason that God invented pollsters was to make astrologers look accurate.”

Of course, taking a small sample to gauge the beliefs of a large group of voters is exactly how the science of polling works.