Mitt Romney said the current Republican presidential campaign has sunk to “a new low” led by the name-calling Donald Trump and pledged in an exclusive TODAY interview to do whatever he could to stop the current front-runner from becoming the GOP nominee.

“There’s no question I’m going to do everything within the normal political bounds to make sure we don’t nominate Donald Trump,” he said Friday, a day after he helped cement the wide division of the Republican Party over Trump. “ I think he would be terribly unfit for office. I don’t think he has the temperament to be president and so I want to see one of the other three [Republican candidates] become the nominee.”

In a speech Thursday, Romney described Trump as a “phony” candidate who would pose a danger to the country if elected. Trump responded by calling Romney "a failed candidate" and a hypocrite who sought his endorsement during Romney's 2012 campaign, which he lost to President Obama.

Mitt Romney TODAY

Shortly after Romney condemned both Trump and the angry movement he inspired, Arizona Sen. John McCain also delivered a strong rebuke against the current front-runner. The extraordinary criticism by the past two Republican presidential nominees represented the sharpest break within the party by the establishment wing of the candidate who appears to have locked this year's White House nomination.

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Romney told TODAY’s Matt Lauer that he decided to speak out because “I couldn’t stand silent anymore” after watching Trump’s increasingly hostile campaign antics and listening to vulgar statements he's made.

He also made clear that his rebuke of Trump had nothing to do with an intention to enter the Republican race himself.

“I’m not running for president and I won’t run for president,” he said. Instead, he believes one of Trump’s rivals has the ability to unite Republicans.

“The people who can save this party are Ted Cruz, Marco Rubio or John Kasich,” Romney said.

He noted that he believes the number of candidates will winnow down to “one or two” following March 15, when the nation holds its next cluster of elections.

“I’m going to supporting that person and doing everything I can to make sure they become the nominee of the party,” he said.

Romney made clear that he has no plans to support Trump – but he also won’t cast a vote for the current Democratic leader, Hillary Clinton.

"I intend to vote for our nominee and I expect that nominee to be a real conservative, a real Republican," he said.

Trump has blasted Romney for his criticism, calling him "a failed candidate" and a "choke artist" and pointing out that Romney actively sought his endorsement during the 2012 campaign.

Romney admitted he welcomed Trump's endorsement at the time.

"I was happy to have it... I was looking for as many endorsements as I could possibly have," he said. But he pointed out many people supported him during that race.

"There are a lot of folks who endorsed me that I would not want to see as president."

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