Mitt Romney on Friday became the highest-profile Republican to vow not to vote for Donald TrumpDonald John TrumpKey takeaways from the Arizona Senate debate Major Hollywood talent firm considering rejecting Saudi investment money: report Mattis says he thought 'nothing at all' about Trump saying he may leave administration 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.
 
Marco RubioMarco Antonio RubioDating app for Trump supporters leaked its users data on launch day: report Overnight Defense: Trump says 'rogue killers' could be behind missing journalist | Sends Pompeo to meet Saudi king | Saudis may claim Khashoggi killed by accident | Ex-VA chief talks White House 'chaos' | Most F-35s cleared for flight Democrats torch Trump for floating 'rogue killers' to blame for missing journalist MORE joined rivals Ted CruzRafael (Ted) Edward CruzBeto O'Rourke will not share million he raised with other Dem Senate candidates Election Countdown: Cruz, O'Rourke fight at pivotal point | Ryan hitting the trail for vulnerable Republicans | Poll shows Biden leading Dem 2020 field | Arizona Senate debate tonight Donald Trump Jr. blasts Beto O’Rourke: ‘Irish guy pretending to be Hispanic’ MORE and John Kasich at the end of the GOP debate Thursday night pledging to vote for Trump if he was the 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.
 
 
“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."