Mitt Romney on Friday became the highest-profile Republican to vow not to vote for Donald TrumpDonald TrumpFundamentals or euphoria? Both fueled post-election stock surge Freedom Caucus founder: GOP health plan did not meet campaign promises Former US envoy: No good military options against North Korea MORE if the controversial businessman becomes the GOP presidential nominee.

“I’ll either vote for a conservative who runs or I’ll write in the name of a conservative," Romney said during an interview on the "Fox Business Network" on Friday.

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"I cannot in good conscience vote for a person who has been as degrading and disruptive and unhinged as I’ve seen Donald Trump be," Romney told host Neil Cavuto. 
 
The position could provide some cover for Republicans who have criticized Trump harshly but felt compelled to voice support for the potential GOP nominee.
 
 
On Friday, Rubio chided debate moderators for asking the question, insisting Trump could "never unite our party." Later, he vowed not to vote for Trump "in the Republican primary."

"I’m going to vote for the nominee, but it’s not going to be Donald Trump," Rubio said on a radio program.

“I can’t even imagine that, and I don’t even want to imagine that right now, to be honest with you. I don’t believe it’s ever going to happen. It’s one of those bridges you hope you never have to cross," he added.

At least two dozen Republican politicians, pundits and operatives have said they won't back Trump as the nominee, according to a tally from The Hill, including Sen. Ben Sasse (R-Neb.) and a few other lawmakers.
 
Trump and Hillary ClintonHillary Rodham ClintonDemocrats step up calls that Russian hack was act of war Comet Ping Pong shooter pleads guilty Time for 'J. Edgar' Comey to take his leave MORE have solidified their positions as the front-runners for the Republican and Democratic nominations, respectively, but Romney indicated Friday he wouldn't support either one.
 
“If those are my only two choices, I’d vote for a conservative on the ballot, and if there weren’t one that I was comfortable with, I would write in a name,” Romney said on Bloomberg TV's "With All Due Respect."
 
“I think there will be a lot of people who would be very troubled with those choices,” Romney said, comparing it to asking someone if they wanted to "drink the poison or take the bullet."