Sen. Mitt Romney (R-UT) announced on Wednesday that he will vote to convict President Trump of one charge, abuse of power, distinguishing himself as the first Republican to support removing the president from office.

In an emotional address on the Senate floor, Romney said Trump is “guilty of an appalling abuse of public trust” and that he made his decision out of an “inescapable conviction that my oath before God demanded it.”

He called Trump’s actions “a flagrant assault under electoral rights, our national security, and our fundamental values. Corrupting an election to keep one’s self in office is perhaps the most abusive and destructive violation of one’s oath of office that I can imagine.”

Romney delivered his address to a mostly empty Senate chamber. A few of his Democratic colleagues, including Sen. Brian Schatz (HI) and Sen. Chris Murphy (CT), stayed to listen to his remarks. As the Utah senator excoriated the president and talked about his duty to his oath, it sunk in for them that Romney might actually vote to convict. Schatz dabbed his eyes with a tissue; Murphy’s jaw dropped. The lone Republican watching, Sen. Roger Wicker of Mississippi, got up and left midway through Romney’s remarks.

The initial reaction among Romney’s GOP Senate colleagues, at least publicly, was indifference rather than indignation. “It is what it is,” Sen. Josh Hawley (R-MO) responded when asked about Romney’s vote.

Romney told The New York Times earlier on Wednesday that he believed “the case was made” and that he would vote against the second article of impeachment, obstruction of Congress, arguing that House Democrats failed to secure testimony and other evidence they sought to make their case.

“I believe that attempting to corrupt an election to maintain power is about as egregious an assault on the Constitution as can be made,” Romney said, adding, “And for that reason, it is a high crime and misdemeanor, and I have no choice under the oath that I took but to express that conclusion.”

The Senate is expected to acquit Trump on both impeachment charges in a vote on Wednesday afternoon.

Romney reportedly acknowledged that he would suffer “unimaginable” political ramifications for his decision, especially from Trump loyalists within his own party. “I recognize there is going to be enormous consequences for having reached this conclusion,” Romney said.

In an interview taped prior to his announcement, Fox News anchor Chris Wallace told Romney, “You realize this is war,” adding, “Donald Trump will never forgive you for this.”

“I know in my heart that I’m doing what’s right,” Romney responded. “I understand it will be substantial. And I have to recognize that it was one or the other. One is to say I don’t want to face the blowback, not just from the president but from my party, my state, from Republican voters.”

Donald Trump Jr. was quick to mock Romney for his decision, posting a picture on Instagram of the senator wearing jeans. “MOM JEANS... Because you’re a pussy,” he captioned the photo. He wrote that Romney was “forever bitter that he will never be POTUS” and was “too weak to beat the Democrats... so he’s joining them now. He’s now officially a member of the resistance & should be expelled from the @GOP.”