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Donald Trump: John McCain "has to be very careful"

Shortly after his wildly unpredictable performance on the Detroit debate stage Thursday night, GOP front-runner Donald Trump spoke with CBS News about the growing opposition to his candidacy from Republican party elders, particularly Mitt Romney and Arizona Sen. John McCain.

When asked how it felt after McCain joined with the 2012 GOP nominee in expressing concerns over Trump's popularity, Trump appeared surprised to learn of McCain's lack of support.

"Oh, he did? Well, that's not nice," he told CBS News' chief White House correspondent Major Garrett. "He has to be very careful."

When pressed on why, Trump tacked on: "He'll find out."

Earlier in the day, McCain released a statement echoing worries voiced by 2012 GOP nominee Mitt Romney during his Thursday press conference in Utah.

"At a time when our world has never been more complex or more in danger...I want Republican voters to pay close attention to what our party's most respected and knowledgeable leaders and national security experts are saying about Mr. Trump, and to think long and hard about who they want to be our next Commander-in-Chief and leader of the free world," McCain, the 2008 Republican nominee, had said.

Still, McCain spokesperson Rachael Dean told CBS News on Thursday that McCain still intends to support the nominee of the Republican Party.

Romney, for his part, had called Trump "very, very not smart" when it came to foreign policy issues, and predicted that with the billionaire in charge of the country, "the prospects for a safe and prosperous future are greatly diminished."

Trump fired back at Romney Thursday night, telling Garrett that the former Massachusetts governor "made a fool out of himself" in 2012.

"He disappeared, he choked, something went wrong with him and I wasn't happy about it and neither were a lot of other people," Trump said.

Trump also hit rival Marco Rubio, who went after the businessman with gusto on the debate stage.

"I think I'm going to do well in Florida," he predicted, largely because "they have an absentee senator."

"He doesn't vote. He doesn't show up anywhere," Trump said. "If I were a person from Florida -- they've been defrauded. They've literally been defrauded by Marco Rubio because he doesn't go to vote."

CBS News' Walt Cronkite contributed to this report.