Mitt Romney launched a new attack on now-presumptive GOP nominee Donald TrumpDonald John TrumpScarborough mocks 'Deflection Don' over transgender troop ban Pelosi condemns Trump's 'cowardly, disgusting' ban on transgender troops Trump moves to ban most transgender people from serving in military MORE Friday, but is standing by his decision not to jump into the race as a third-party candidate. 
"I think you're not going to find a credible candidate actually running as a third-party contender," Romney told CNN's Wolf Blitzer in an interview in Park City, Utah. "I'd like to see someone run, but that's not likely."
Asked if he'd personally seek such a candidacy, Romney insisted nothing has changed.
"No, that's not something I'm going to be doing," he said. 
The former GOP nominee said he doesn't regret not running again but said he would have put up a fight against Trump.
"I thought it was time for someone new. I'm glad I wasn't out there with Donald Trump," he said. "Had I been in the race, I can assure you I would have taken him on."
"I'm sure he believes he would have been successful pushing me aside just like he did others in part because I would have been seen as an establishment Republican," Romney added. 
Romney offered a scathing evaluation of Trump's "character," describing his past comments and policies as evidence that he'd be a "dangerous" president, saying that he is "too great a departure from the values of our country."

“Presidents have an impact on the nature of our nation, and trickle-down racism, trickle-down bigotry, trickle-down misogyny, all these things are extremely dangerous to the heart and character of America," he said. 
When asked if he thinks Trump is racist, Romney responded: "Oh, I think his comments time and again appeal to the racist tendency that exists in some people, and I think that's very dangerous.”
Romney condemned Trump's recent attacks on a federal judge — Trump has claimed Judge Gonzalo Curiel cannot impartially preside over a Trump University fraud case because of his Mexican heritage — and said he doesn't "want to be associated with that in any way, shape or form."
"I don't think there's anything I'm looking for from Mr. Trump to give him my support," Romney said. "He's demonstrated who he is."
But Romney declined to rebuke Speaker Paul RyanPaul Davis RyanYou just can't keep good health policy down Trump blasts Congress for sending him omnibus bill that 'nobody read' Students bash Congress for inaction on gun control MORE, his former running mate, for continuing to support Trump despite calling his remarks on the judge "textbook" definition of a racist comment.
"I wish everybody in the Republican Party had rejected Mr. Trump and chosen someone else," Romney said. "But my choice is different than that of the other people, and I'm certainly not going to argue with them about their choice."
Romney, who once predicted that there is a "bombshell" in Trump's unreleased tax returns, continued to highlight the potential problems in the documents.
"I think he's calculated that he could get support even if he shot someone, but if he'd released his taxes, he'd lose support," Romney said, referring to Trump's comment earlier this year that he could shoot someone on Fifth Avenue and not hurt his campaign.
"So there's something in those taxes that's even worse than shooting someone on Fifth Avenue," Romney said, speculating Trump's taxes may show "income from unsavory sources" or "unsavory" connections.
"Who knows what it could be?" said Romney, who was similarly dogged to release his tax returns in the 2012 election. 
"There's no question in my mind, he will never release his tax returns," Romney continued. "He will follow one excuse after another to say why he can't."
Trump has maintained that he is not releasing his returns because he is under an audit, although the IRS has said nothing prevents him from releasing them.
Romney said he would not be voting for either Trump or presumptive Democratic nominee Hillary ClintonHillary Diane Rodham ClintonRepublicans invest nearly 0,000 in red Arizona district Al Franken: Sessions firing McCabe ‘is hypocrisy at its worst’ Papadopoulos encouraged by Trump campaign staffer to make contact with Russians: report MORE and would instead write in the name of another Republican. He praised Libertarian vice presidential candidate former Massachusetts Gov. Bill Weld and said he would look into the platform of Libertarian nominee, former New Mexico Gov. Gary JohnsonGary Earl JohnsonWithout ranked voting, Pennsylvania's slim margins hide voters' preferences If weed is no longer a crime, why are people still behind bars? Gary Johnson: Trump admin marijuana policy shift could cost him reelection MORE.
Romney emerged as one of the loudest anti-Trump Republicans during the primary season, calling him a "phony" and a "fraud" in a blistering speech, and he worked to garner support for both Ted CruzRafael (Ted) Edward CruzLesson from special election: Run on Social Security, Medicare and lower drug prices Conservatives balk over funding bill ahead of shutdown  Confirmation fight over Trump pick exposes blurred lines in GOP-LGBT activism MORE and John Kasich.