SALT LAKE CITY, Utah -- Mitt Romney opened his speech by citing Ronald Reagan's argument before the 1964 election that it was "a time for choosing" -- previewing his expected criticism of GOP front-runner Donald Trump by saying he planned to look inward within his own party.
"I'm no Ronald Reagan, and this is a different moment in time, but I believe with all my heart and soul that we face another time of choosing -- one that will have profound consequences for the Republican Party and more importantly, for our country," he said.
Romney wasted no time taking direct aim at Trump.
"On the other hand, if we make improvident choices, the bright horizon I foresee will never materialize," he said. "Let me put it plainly, if we Republicans choose Donald Trump as our nominee, the prospects for a safe and prosperous future are greatly diminished."
Romney called Trump's policy proposals "flimsy, at best," and said he'd trigger a trade war, drive up the deficit and lead the nation into a recession.
"Even though Donald Trump has offered very few specific economic plans, what he has said is enough to know that he would be very bad for American workers and American families," he said.
"Now I know you say, 'Isn't he a huge business success, and doesn't he know what he's talking about?' No he isn't, and no he doesn't. His bankruptcies have crushed small businesses and their workers. He inherited his business; he didn't create it."
Romney offered praise for the economic plans of Florida Sen. Marco Rubio, Texas Sen. Ted Cruz and Ohio Gov. John Kasich.
"One of these men should be our nominee," he said.
Romney cast Trump's foreign policy proposals as "recklessness in the extreme," pointing to his suggestion on "60 Minutes" that the United States should let ISIS take out Syria's Bashar al-Assad.
"Now Donald Trump tells us he is very, very smart. I'm afraid that when it comes to foreign policy, he is very, very not-smart," he said.
Romney said that "dishonestly is Donald Trump's hallmark," pointing to his "bullying, the greed, the showing off, the misogyny, the absurd third-grade theatrics."
"There's a dark irony in his boasts of his sexual exploits during the Vietnam war, while at the same time, John McCain, who he has mocked, was in prison being tortured," he said.
He lambasted Trump's assertions that he opposed the war in Iraq and saw Muslims celebrating 9/11 in New Jersey.
"He's not of the temperament of the kind of stable, thoughtful person we need as leader. His imagination must not be married to real power."
Romney made an effort to pre-but Trump's response to his speech.
"Watch, by the way, how he responds to our speech today. Will he talk about our policy differences, or will he respond with every low-road insult?" Romney said.
Romney predicted Trump's exchange about white supremacists with CNN's Jake Tapper last Sunday on "State of the Union" would damage him in the general election.
"The video of the infamous Tapper-Trump exchange on the Ku Klux Klan will play 100,000 times on cable and who knows how many billion times on social media," he said.
He called on Trump to release his tax returns, predicting another "bombshell."
"I predict that he doesn't give much of anything to our disabled, to our veterans," he said.
He called on Trump to also ask The New York Times to release the recording of an off-the-record conversation he had with the newspaper's editorial board.
**Fox 8's Gabe Spiegel will be in Detroit for the debate. Be sure to tune in for live reports beginning on Fox 8 News at 4 p.m. and other updates all day right here on Fox8.com**