Mitt Romney, then the GOP presidential candidate, at a rally in Yardley, Penn. on Nov. 4, 2012. (Melina Mara/The Washington Post)

SALT LAKE CITY — Mitt Romney, the 2012 Republican presidential nominee, plans to deliver a sharp broadside against Donald Trump today, slamming the GOP’s leading candidate as pandemonium sweeps the party.

In a forceful, top-to-bottom indictment of Trump, Romney will call on fellow Republicans to reject the billionaire businessman’s candidacy in an election “that will have profound consequences for the Republican Party and more importantly, for the country.”

“Donald Trump is a phony, a fraud,” Romney will say, according to a speech prepared for delivery Thursday morning at the University of Utah’s Hinckley Institute of Politics. “His promises are as worthless as a degree from Trump University. He’s playing the American public for suckers: He gets a free ride to the White House, and all we get is a lousy hat.”

Mitt Romney and Donald Trump shake hands during a news conference held by Trump to endorse Romney in 2012. (Ethan Miller/Getty Images)

Romney, the 2012 Republican presidential nominee, briefly considered running again before announcing in January that he would take a pass. His speech in Utah, where he has a home, comes at a critical juncture for the Republican Party, with Trump’s march to the nomination setting off alarm among GOP leaders who fear that he would lose the general election and tarnish the party’s brand for a generation.

During a town hall meeting in New Hampshire, GOP presidential candidate Donald Trump slammed 2012 presidential nominee Mitt Romney, saying that he “choked.” (Reuters)

“In 1964, days before the presidential election, Ronald Reagan went on national television and challenged America that it was a ‘Time for Choosing,'” Romney is expected to say. “He saw two paths for America, one that embraced conservative principles dedicated to lifting people out of poverty and helping create opportunity for all, and the other, an oppressive government that would lead America down a darker, less free path.

“I’m no Ronald Reagan and this is a different moment, but I believe with my heart and soul that we face another time for choosing, one that will have profound consequences for the Republican Party and more importantly, for the country.”

Romney has not endorsed a candidate in the 2016 race, and his associates said Wednesday that he was unlikely to do so in the immediate future. He has kept in touch with two remaining candidates, Sen. Marco Rubio of Florida and Ohio Gov. John Kasich.

“Of the remaining candidates,” the prepared remarks say, “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.”

As results showed Donald Trump leading in at least six states on Super Tuesday, Sens. Ted Cruz (R-Tex.) and Marco Rubio (R-Fla.) argued that nominating him would be bad for the Republican party. Here are key moments from their speeches following the March 1 races. (Sarah Parnass/The Washington Post)

The former presidential candidate has emerged in recent days as an aggressive critic of Trump, using Twitter to call on the billionaire to release his tax returns and to denounce Trump’s refusal to disavow the endorsement of his campaign by former Ku Klux Klan leader David Duke.

Trump, in turn, has taken to attacking Romney on Twitter.

In an interview with MSNBC’s “Morning Joe” on Thursday, Trump was critical of Romney and his presidential campaign, calling the former candidate a “catastrophe.”

“First of all, he’s a man, who as you know, begged me, and I mean begged me for my endorsement four years ago,” Trump said. “OK, so that’s fine. He failed in his campaign, it was a horribly run campaign. Republicans didn’t even go out to vote. He was a disaster the last month, month and a half, he wasn’t on television, it was almost like he was lost, and he ran one of the worst campaigns, as you know, in presidential history. That was an election that should have been won by the Republicans. He was a catastrophe.”

Several of Romney’s friends, allies and former donors are involved in efforts to stop Trump, launching and funding super PACs airing ads against the businessman, in Florida, Ohio and elsewhere.

Speaking to students last month at Babson College in Massachusetts, Romney said he shared the feeling of many Americans that Washington has failed them, and he urged national leaders to tackle big problems such as climate change, poverty, education and income inequality.

“We’re just mad as hell and won’t take it anymore,” Romney said of the national electorate. He harshly criticized “the failure of current political leaders to actually tackle major challenges, or to try at least, or to go out with proposals.”

According to Romney’s Thursday remarks, Trump’s “domestic policies would lead to recession. His foreign policies would make America and the world less safe. He has neither the temperament nor the judgement to be president. And his personal qualities would mean that America would cease to be a shining city on a hill.”

Trump, Romney is expected to say, “relishes any poll that reflects what he thinks of himself. But polls are also saying that he will lose to Hillary Clinton.”

Also in the prepared speech: “A person so untrustworthy and dishonest as Hillary Clinton must not become president. But a Trump nomination enables her victory.”

Philip Rucker and Robert Costa contributed to this report, which has been updated. Larimer reported from Washington.