Utah Sen. Mitt Romney will defy his fellow Republicans and vote to convict and remove President Donald Trump from office over withholding military aide from Ukraine as part of a scheme to force an investigation into former Vice President Joe Biden and his son, Hunter, who sat on the board of Burisma, a Ukrainian energy company.

Romney announced on the Senate floor Wednesday afternoon, just hours ahead of the final vote on impeachment, that he would vote to convict Trump on the charge he abused the power of his office for his own personal gain.

“The president is guilty of an appalling abuse of the public trust,” an emotional Romney said. “What he did was not ‘perfect.’ No, it was a flagrant assault of our electoral rights, our national security, and our fundamental values.”

Romney’s vote against Trump will be historic, as it will become the first time in American history a senator has voted to remove a president from the same political party in a Senate impeachment trial.

Ronna McDaniel, the chair of the Republican National Committee and Romney’s niece, said in a statement she disagreed with her uncle’s decision and that “President Trump did nothing wrong.” Donald Trump Jr., the president’s oldest son, declared Romney a “member of the resistance” on Twitter and called on Republicans to expel him from the party.

The final vote in what has been by historic standards a swift impeachment trial is expected to take place Wednesday afternoon at 4 p.m. Senators spent the bulk of the last few days delivering speeches highlighting their individual decisions, with nearly all falling along party lines whether to acquit the president or convict and remove him from office.

Three moderate Democrats — Doug Jones of Alabama, Kyrsten Sinema of Arizona, and Joe Manchin of West Virginia — all announced on Wednesday they would vote to convict the president and remove him from office.

The final vote will come just a few days after Democrats failed to pass a motion to subpoena witnesses with first-hand knowledge of Trump’s actions, such as former national security adviser John Bolton. In that vote, just two Republicans — Romney and Sen. Susan Collins of Maine — voted with Democrats.

Here’s what we know about what is expected to be the final day of Trump’s impeachment trial:

What time will the final impeachment vote take place?

The Senate trial is officially in recess until Wednesday at 4 p.m., when senators are expected to cast their final votes on the two articles of impeachment.

Prior to that, senators will continue to give speeches on the Senate floor explaining their positions and how they intend to vote, something members of both parties pushed for and have been doing since Monday afternoon. Each senator has up to 10 minutes to talk.

What is Trump charged with?

Trump was formally charged by the House with two counts: Abuse of power and obstruction of Congress.

Trump is accused to using the office of the presidency for personal political gain by withholding military aide from Ukraine as part of a scheme to force an investigation into the Bidens. The obstruction of Congress charge stems from what Democrats described as his stonewalling of Congress by blocking access to witnesses and relevant documents.

“You can’t trust this president to do the right thing. Not for one minute, not for one election, not for the sake of our country," Democratic Rep. Adam Schiff said during his closing arguments on Monday. "He will not change and you know it.”

Trump’s defense team argued that the Democrats have been out to remove Trump from office since the start of his presidency, and that the impeachment trial was their latest attempt to undo the 2016 election and prevent him from being re-elected in 2020.

“Leave it to the voters to choose,” White House counsel Pat Cipollone said in his closing arguments.

How many votes would it take to remove Trump from office?

A two-thirds super majority of the Senate (67 votes) is required to convict Trump and remove him from office.

Republicans hold a 53-47 majority in the Senate, so Democrats would need at least 20 Republicans to cross party lines.

How are Pennsylvania’s senators expected to vote?

Pennsylvania’s two senators — Democrat Bob Casey and Republican Pat Toomey — are expected to vote along party lines when the final votes are cast Wednesday afternoon.

Casey said he would vote to convict Trump on both counts in a statement issued Tuesday:

There is no doubt that President Trump withheld military aid and a vital White House meeting from Ukraine, in order to coerce its President into announcing a sham investigation of a political rival and a debunked conspiracy theory about the 2016 election. It has also been established that he solicited foreign interference in the 2020 election and then further abused his power by covering it up and obstructing Congress’ well-predicated investigation.

Toomey explained his decision in an op-ed for the Inquirer:

The president’s actions were not “perfect.” Some were inappropriate. But the question before the Senate is not whether his actions were perfect. It is whether they constitute impeachable offenses that justify removing a sitting president from office for the first time and forbidding him from seeking office again.

What channels will offer live coverage of the impeachment vote?

C-SPAN, CNN, Fox News, MSNBC, and WHYY-TV will all offer live coverage of Wednesday’s impeachment proceedings, but it’s unclear which broadcast networks will break into their normal coverage to cover the final vote.

Regardless of their broadcast plans, ABC News, CBS News, and NBC News will all stream live coverage of the impeachment trial on their respective digital platforms.

The Associated Press contributed to this article.