Former Republican presidential nominee Mitt Romney offered a scathing assessment of Donald Trump's candidacy, saying if he becomes the GOP's nominee, "the prospects for a safe and prosperous future are greatly diminished."
Romney told the audience at the University of Utah Thursday morning that the billionaire developer is not what he seems, saying, "A business genius he is not."
Romney said the "bullying, the showing off and misogyny and third grade theatrics" Trump has displayed on the campaign trail show Trump does not have "the temperament of a stable, thoughtful leader" the country needs.
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The 2013 GOP nominee offered a series of predictions about Trump, saying there are bombshells in his tax releases he would never make public and his immigration talk "was just that."
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"If I’m right then you’ll have all the proof that you’ll need to know that Donald Trump is a phony," Romney said.
Romney said, "Trump's bombast is already alarming our allies and fueling the enmity of our enemies." He said Trump insulting all Muslims will keep many of them from working with the U.S. to fight terrorism and his idea to let "ISIS take out Assad" is reckless.
"Donald Trump tells us that he is very, very smart," he said. "I'm afraid that when it comes to foreign policy he is very, very not smart."
He later brought up Trump's claims that he saw Muslims in New Jersey celebrating 9/11. "His imagination must not be married to real power," Romney said.
Trump's Twitter account was silent during Romney's speech, with the candidate having tweeted earlier that he was en route to Portland, Maine. But Dan Scavino, a Trump senior adviser and director of social media, responded on Twitter that Romney was "very bitter."
"I don't think he is a fan of the #TrumpTrain," he wrote.
Trump's son Donald Trump Jr also panned Romney as a "loser."
At a rally in Maine later Thursday, Trump said Romney was a "failed candidate" who had begged him for his endorsement in 2012.
"I could have said, 'Mitt drop to your knees,' and he would have dropped to his knees," Trump said.
Romney also addressed his past endorsement by Trump on Twitter.
"If Trump had said 4 years ago the things he says today about the KKK, Muslims, Mexicans, disabled, I would NOT have accepted his endorsement," Romney wrote.
Former Alaska Gov. Sarah Palin responded to Romney's attack with a Facebook video questioning his conservative credentials and telling Trump not to "take the bait."
“The ‘machine's’ deception and nonsensical attack on Trump isn't really an attack on the candidate, it's an attack on conscientious, hardworking, patriotic Americans who know we need a revolution to stop the complicit politicians who are fundamentally transforming America. We found the revolutionary,” she said. “Donald Trump is the shock the Permanent Political Class needs to wake them up... to destroy their selfish cabal... to respect the will of the people... to make America safe and solvent... to make America great again.”
“Don't take the bait, Mr. Trump. It's not about you. It's about us. And we've got your back,” Palin said.
In turning up the rhetoric, Romney cast his lot with a growing chorus of anxious Republican leaders — people many Trump supporters view as establishment figures — in trying to slow the New York real estate mogul's momentum.
Romney branded Trump as "a phony, a fraud" whose "promises are as worthless as a degree from Trump University" in his speech.
"The only serious policy proposals that deal with the broad range of national challenges we confront today, come from Ted Cruz, Marco Rubio, and John Kasich," Romney said of Trump's GOP rivals. "One of these men should be our nominee."
Following Romney's speech, Sen. John McCain said in a statement that he shares Romney's concerns and added: "I would also echo the many concerns about Mr. Trump’s uninformed and indeed dangerous statements on national security issues that have been raised by 65 Republican defense and foreign policy leaders."
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"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 said.
Earlier on Thursday, Trump called Romney a "stiff" in a phone interview on NBC's "Today" show. "He was going against a president that should’ve been beaten... The problem is no one came out to vote for Mitt Romney," Trump added.
He said "millions and millions of people" are joining the Republic party because "they're energized" by his message.
Romney has been chipping away at Trump in recent days, but the speech Thursday was his most forceful statement yet and comes as panicked GOP leaders say they still have options for preventing the billionaire from winning the GOP nomination.
It was unclear what impact his words would have with voters deeply frustrated by their party's leaders.
Trump, meanwhile, was setting his sights on the general election. His campaign reached out to House Speaker Paul Ryan's office to arrange a conversation between the two men, and urged Republican leaders to view his candidacy as a chance to expand the party.
"Why can't the leaders of the Republican Party see that I am bringing in new voters by the millions — we are creating a larger, stronger party!" Trump said on Twitter.
Indeed, there was a surge in turnout in Super Tuesday's GOP primaries. While that could typically be a welcome sign for a party that has struggled to attract new voters in recent presidential elections, GOP leaders were privately grappling with the reality that some of those voters were in fact registering their opposition to the Republican establishment.
In his speech Thursday, Romney called this moment a "time for choosing" that will "have profound consequences for the Republican Party and more importantly, for the country."
"Of the remaining candidates," he says, "the only serious policy proposals that deal with the broad range of national challenges we confront have come from Ted Cruz, Marco Rubio, and John Kasich."