Donald Trump's coronation as the GOP's presumptive nominee has caused some prominent Republicans to panic. Or at least some people now formerly known as Republicans.

Lachlan Markay, a writer for the conservative website Washington Free Beacon, burned his Republican voter registration card Tuesday night in a video he posted to Twitter. Markay is one of several prominent conservatives who loudly denounced the party after Trump was declared the presumptive nominee on Tuesday, some of whom are even doing the unthinkable — promising to vote for Hillary Clinton.

On Wednesday, Markay said that he's "definitely sticking with" his decision to leave the Republican party, although he's not exactly happy about it.

"I'm sad to see the Republican Party embrace someone who has so thoroughly repudiated every principle that got me to join the party in the first place," Markay said. "And I'm sad to see people I once respected get behind someone who's so clearly exploiting them for his own personal, political, and financial ambitions."

Ryan Hart, a University of Virginia law student who used to work on Capitol Hill for several Republican congressmen, also divorced himself from the party as soon as it became evident Trump would be the nominee.

"[I] mailed in the form today," Hart said. "I'll be 'unaffiliated' for the first time since I was 18."

Erick Erickson, the high-profile conservative writer and frequent cable news guest, said that he too will leave the party if Trump wins the nomination officially at the party's convention in July.

"If Trump is the Republican Party nominee, I won't be a Republican. I'm not down with white supremacists," Erickson told the Daily Beast.

Trump's unlikely vault to the front of the Republican field has provoked horror from many Republicans throughout this primary election. But now that his position as the party's standard-bearer has been officially solidified (Republican party chairman Reince Priebus confirmed Trump as the "presumptive nominee" Tuesday evening), many of those Republicans are now breaking ranks with their party.

Markay, Hart and Erickson were joined Tuesday night and into Wednesday morning by several other Republican activists, campaign staffers and writers, who now find the "R" on their voter cards embarrassing.

But while some conservatives, like Markay or Hart, are changing their registration to unaffiliated or plan to vote for a third party in the November general election, others are going even further, vowing to vote for the candidate who has long been the Republican's number one enemy.

The list of Republicans now declaring that they will support Clinton over Trump includes Mark Salter, a former top advisor to Republican Senator John McCain's presidential campaign.

"The GOP is going to nominate for President a guy who reads the National Enquirer and thinks it's on the level," Salter wrote on Twitter Tuesday night. "I'm with her."

A former Republican Senate staffer, Joseph Shonkwiler, is also making the move over to Clinton.

"I am a lifelong #Republican, but I am ashamed of #GOP today," Shonkwiler tweeted Wednesday. "Count me in for @HillaryClinton #NeverTrump #ImWithHer"

Ben Howe, a prominent writer at the ultra-conservative website Red State, too, is on the list. Howe, who who has been firmly in the Never Trump camp since the candidate announced his candidacy last June, went further after Trump's victory Tuesday night. Howe declared that he will support Clinton over his party's choice and departed the GOP in a fiery blaze of tweets.

On Wednesday, Howe described his decision more as a vote against Trump, rather than an endorsement of Clinton.

"Embracing Trump by unifying around him would be embracing his insane, pathological, lying, manipulative, destructive existence and saying 'hey! That's our guy!' " Howe said. "I can't be a part of that."

Republicans have long feared that Trump could prompt an exodus from the party if he becomes the nominee. This not only could cost the Republicans the White House, but could very well cause the GOP to lose control of every other branch of the federal government in the 2016 election, including majorities in the House and Senate, and thus, a seat on the Supreme Court.

The party won't fully know how many of their members will actually cast a ballot for Clinton, or just sit out the election altogether, until November, but early polling suggests that it might not be an inconsequential chunk of the party. According to a recent Reuters poll, conducted before Trump secured his presumptive nominee status, fully a third of Republican voters said they would not support Trump if he was the party's nominee. Additionally, 13 percent of Ted Cruz supporters said they would vote for Clinton over Trump in the general election, while 25 percent of John Kasich supporters said the same, according to a poll conducted by Morning Consult just this week.

Trump's surprising showing in 2016 has caused some soul-searching for these Republicans. Many, like Hart, have been loyal members of the party their entire lives, but are now unhappily being forced to question their political identity. Hart described his emotions on Wednesday as being "all over the place."

"I'm sad to have to leave a party that I worked hard for and that I think could do a lot of good if it got its act together," Hart said. "I feel terrible for my friends who are still working in politics. They have a terrible decision to make."