Former US presidential candidate Mitt Romney attacked 2016 Republican front-runner Donald Trump on 3 March, describing Trump's "personal qualities" as undesirable and his policies as "very, very not smart". In an unusually harsh speech, party elder Romney warned that former reality TV star Trump would likely lose to possible Democratic candidate Hillary Clinton in the 8 November election if he becomes the Republican nominee.

Romney said: "Think of Donald Trump's personal qualities – the bullying, the greed, the showing off, the misogyny, the absurd third-grade theatrics. We have long referred to him as 'The Donald.' He is the only person in the entire country to whom we have added an article before his name, and it wasn't because he had attributes we admired. Now imagine your children and your grandchildren acting the way he does. Will you welcome that?"

Romney's speech in Utah was the spearhead of a mainstream Republican attempt to rein in Trump after he won most states in this week's Republican Super Tuesday nominating contests and took a step towards earning the nomination. The party establishment's strategy risks backfiring by further energising Trump's supporters, many of them white, blue-collar voters. Romney did not endorse any candidate.

"Now, I am far from the first to conclude that Donald Trump lacks the temperament of be president. After all, this is an individual who mocked a disabled reporter, who attributed a reporter's questions to her menstrual cycle, who mocked a brilliant rival who happened to be a woman due to her appearance, who bragged about his marital affairs, and who laces his public speeches with vulgarity. Donald Trump says he admires Vladimir Putin, at the same time he has called George W Bush a liar. That is a twisted example of evil trumping good."

"There is dark irony in his boasts of his sexual exploits during the Vietnam War, while at the same time John McCain, whom he has mocked, was imprisoned and tortured," he added.

Trump, 69 has made his party's establishment uneasy with his abrasive tone and policy positions, including plans to build a wall on the US-Mexican border, deport 11m illegal immigrants and temporarily bar Muslims from entering the country.

"And then what he said about Syria on 60 Minutes. Did you hear this? It was about Syria and Isis, and it has to go down as the most ridiculous and dangerous idea of the campaign season. 'Let Isis take out Assad,' he said, and then we can pick up the remnants. Now think about that: Let the most dangerous terror organization the world has ever known take over a country? This recklessness is recklessness in the extreme. And Donald Trump tells us that he is very, very smart. I'm afraid that when it comes to foreign policy he is very, very not smart," Romney quipped.

Trump dismissed the former Massachusetts governor who lost to Democratic President Barack Obama four years ago. "Mitt is a failed candidate. He failed. He failed horribly. He failed badly," Trump told a rally in Maine and tweeted:

Why did Mitt Romney BEG me for my endorsement four years ago?

— Donald J. Trump (@realDonaldTrump) March 3, 2016

Romney shot back on Twitter saying:

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

— Mitt Romney (@MittRomney) March 3, 2016