NEW YORK - Former Republican presidential nominee Mitt Romney jumped into the party’s fray over Donald Trump on Thursday, blasting the front-runner for the presidential nomination as a ‘phony’ and a ‘fraud’ who would hand the White House over to Hillary Clinton, the Democratic front-runner, in the November 9 national election.

‘His promises are as worthless as a degree from Trump University,’ Romney said in a speech, according to excerpts released by his office. Romney is scheduled to deliver his remarks later Thursday at the University of Utah in Salt Lake City.

Trump, who endorsed Romney in 2012 and is now on the cusp of the Republican nomination himself, wasted no time in hitting back. The billionaire businessman said Romney blew his chance at election - against Democrat Barack Obama - four years ago and is now representing a Republican establishment that has let down its supporters.

‘Failed candidate Mitt Romney,who ran one of the worst races in presidential history,is working with the establishment to bury a big ‘R’ win!’ Trump tweeted. Romney said, ‘His domestic policies would lead to recession. His foreign policies would make America and the world less safe. He has neither the temperament nor the judgment to be president. And his personal qualities would mean that America would cease to be a shining city on a hill.’

Romney is neither expected to endorse a candidate nor announce a third presidential bid of his own, according to media reports. Instead, spoke in broad strokes about the state of the 2016 race for the White House and, of course, deliver a few choice words about Trump.

Trump responded with a cavalcade of tweets against Romney, who sought Trump’s support during his 2012 run. As Trump recalls it, ‘He begged me four years ago for my endorsement - I mean literally begged me,’ he told NBC’s ‘Today.’ ‘And he’s a failed candidate. I mean, frankly I backed him; he failed. He was a horrible candidate.’

In February 2012, Trump praised Romney and introduced him as someone who ‘wouldn’t allow bad things to continue to happen to this country that we all love.’ ‘There are some things that you just can’t imagine happening in your life,’ Romney said, beaming as he accepted Trump’s support. ‘This is one of them. Being in Donald Trump’s magnificent hotel and having his endorsement is a delight. I’m so honored and pleased to have his endorsement.’ But on Thursday, those pleasantries seemed a distant memory.

‘Mitt Romney is a stiff,’ Trump told ‘Today.’ ‘Mitt Romney will not get elected. Mitt Romney failed twice and really failed last time. He was going against a president that should have been beaten.’

Romney, Trump said, had disappeared in the month leading up to the election. ‘This guy disappeared. He went away,’ he said. ‘And he got killed. He got decimated in the election.’ In a separate phone interview on MSNBC’s ‘Morning Joe’ later Thursday morning, Trump labeled Romney a ‘catastrophe’ who is ‘just trying to stay relevant.’

‘I helped him and I raised money for him and I did everything, but he didn’t do the job,’ the real-estate mogul said. ‘He didn’t have the capability to do the job, and he certainly hasn’t gotten any better.’ Trump also renewed his threat to run as an independent candidate, despite his 2015 pledge to remain in the Republican Party and support its nominee.

‘I am watching television and I am seeing ad after ad after ad put in by the establishment knocking the hell out of me, and it’s really unfair,’ he said. ‘But if I leave, if I go, regardless of independent, which I may do - I mean, may or may not. But if I go, I will tell you, these millions of people that joined, they’re all coming with me.’

Trump’s pushback comes as his rivals, Senators Ted Cruz and Marco Rubio, have intensified their attacks ahead of Thursday night’s debate, while a trio of anti-Trump groups have stepped up their fundraising efforts and launched new ads in a coordinated assault portraying the front-runner as untrustworthy and erratic.

The biggest focus is on Florida, a must-win state for Rubio that votes on March 15. Club for Growth, an anti-tax group that has been hammering Trump on the airwaves, has purchased $1.5 million in TV advertising in the state. Another conservative outfit that has been targeting the New York billionaire, American Future Fund, has reserved $1.75 million of commercial time. A third anti-Trump group run by former top Romney aide Katie Packer, Our Principles PAC, is considering advertising there too. As Donald Trump closed in on Republican presidential nomination following his triumph in seven US states on Super Tuesday, the party’ s strategists and donors have begun taking steps with a sense of urgency  to halt his campaign that has exacerbated religious, racial, ethnic and gender tensions.

Club for Growth Action, an anti-tax group,  launched a new $1.5 million ad in Florida, casting Trump as a lousy businessman who ‘hides behind bankruptcy laws to duck paying his bills.’ The organization’s leaders say they also are likely to withhold endorsements and fundraising help from any Republican congressional candidate who backs the brash billionaire businessman.

Florida’s delegate-rich primary is March 15. ‘Time is running out,’ said Club for Growth spokesman Doug Sachtleben. ‘Trump could cost us a good shot at the White House, the Senate majority, and ultimately, the Supreme Court.’

The Republican 2012 nominee Mitt Romney, who has become an increasingly loud anti-Trump voice in recent days, also plans to deliver a major address about the presidential contest later on Thursday, just hours before Trump and three other Republican candidates are slated to take the debate stage in Detroit, NBC News and other news organizations reported Wednesday.

Retired neurosurgeon Ben Carson announced Wednesday that he will not participate in the debate, as he sees no ‘path forward’ for his campaign. A Trump nomination would be ‘a disaster’ for Senate Republican candidates,  Rob Jesmer, a Republican strategist and former executive director of the National Republican Senatorial Committee. ‘People are just waking up to that reality in the last few days.’

‘His microphone is bigger than anyone’s in the whole country,’ Jesmer said and Senate candidates seeking to win over moderate voters in swing states would be forced answer for Trump’s controversial statements and positions on issues such as deporting 11 million unauthorized immigrants from the country.

Meanwhile, Republican loyalists have raised the possibility of the party splintering and choosing a third-party option if Trump wins the nomination. ‘There are a lot of people who just cannot see themselves supporting Trump, Christine Todd Whitman, a former New Jersey governor, told National Public Radio on Wednesday. In Tuesday’s Super Tuesday primary elections, Republican presidential candidate and US Senator Ted Cruz, an ultra conservative,  won his delegate-rich home state of Texas and neighboring Oklahoma as well as Alaska.

Florida Senator Marco Rubio notched just one victory in Minnesota. Cruz’s and Rubio’s victories were unable to alleviate the alarm among party  backers, who fear the party is headed toward an annihilating defeat in the general presidential elections in November.

‘Republicans are reaping the whirlwind right now, and Democrats should seize the chance to show Americans an alternative to Mr Trump’s politics of rage, and an image of themselves to be proud of, not shrink from,’ The New York Times observed. Trump’s latest wins also compounded the problem for a party whose leaders are both critical of many of Trump’s positions and values and skeptical he can defeat the Democratic Party rivals, former Secretary of State Hillary Clinton and Senator Bernie Sanders.

A recent CNN/ORC poll found that both Clinton and Sanders would easily defeat Trump if the November 8 election were held now. Clinton, who enjoys overwhelming African-American support, won in Alabama, Arkansas, Georgia, Massachusetts, Tennessee, Texas and Virginia. Sanders notched wins in his home state of Vermont, Oklahoma, Colorado and Minnesota. Sanders, a self-styled democratic socialist, has vowed to press on with his well-funded campaign that has made shrinking the income gap between rich and poor and providing universal healthcare a central issue of the Democratic contest.