Video by Associated Press

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On Wednesday, Sen. Mitt Romney of Utah made history by becoming the first US Senator to vote to convict the president of his own party in an impeachment trial, blindsiding and angering Republicans.

Romney announced his shocking decision in a speech on the Senate floor shortly before the Senate is expected to vote to acquit Trump on two articles of impeachment for abusing his office and obstructing Congress.

Romney's vote was especially notable given his stature in Republican politics. The former governor of Massachusetts, Romney ran for president twice and was the Republican presidential nominee in 2012.

His niece, Ronna McDaniel, is also the Chairwoman of the Republican National Committee, which is firmly behind Trump and helping fund his re-election campaign.

"This is not the first time I've disagreed with Mitt, and I imagine it will not be the last. The bottom line is President Trump did nothing wrong, and the Republican Party is more united than ever behind him," McDaniel said a statement following Romney's announcement. "I, along with the GOP, stand with President Trump."

The Republican Party also blasted out a press release following Romney's decision, titled, "Mitt Romney turns his back on Utah."

Here's how key Republican figures reacted:

Trump's son Donald Trump Jr. suggested Romney should be expelled by the Republican caucus

Mitt Romney is forever bitter that he will never be POTUS. He was too weak to beat the Democrats then so he’s joining them now. He’s now officially a member of the resistance & should be expelled from the @GOP. — Donald Trump Jr. (@DonaldJTrumpJr) February 5, 2020

Rep, Jim Jordan, the ranking member of the House Oversight Committee and a crucial Trump ally, called it "wrong."

Jim Jordan on Romney: “wrong wrong wrong move” — Jake Sherman (@JakeSherman) February 5, 2020

Former congressman Newt Gingrich skewered Romney and pointed to comments he made in 1994 criticizing former President Ronald Reagan.

Just remember Mitt Romney 1994: “Look, I was an independent during the time of Reagan-Bush. I’m not trying to return to Reagan-Bush." Nothing surprising in today’s announcement. If someone won’t defend President Reagan they probably won’t defend President Trump. — Newt Gingrich (@newtgingrich) February 5, 2020

In a speech on the Senate floor, Romney said he expected harsh blowback from his fellow colleagues.

"Does anyone seriously believe that I would consent to these consequences, other than from an inescapable conviction that my oath before God demanded it of me?" he said in his floor speech.

The Senate will hold a final vote on whether to convict or acquit Trump beginning at 4 p.m. ET on Wednesday.

Trump was impeached in December and charged with abuse of power and obstruction of Congress. Both articles of impeachment relate to his efforts to strong-arm Ukraine into interfering in the 2020 election while withholding $391 million in vital military aid and dangling a White House meeting that Ukrainian President Volodymyr Zelensky desperately sought and still hasn't gotten.

At the center of the impeachment inquiry was a July 25 phone call during which Trump repeatedly pressured Zelensky to investigate former Vice President Joe Biden and his son, Hunter, over the latter's employment on the board of the Ukrainian natural-gas company Burisma Holdings.

Trump also asked Zelensky to help discredit the Russia probe by investigating a bogus conspiracy theory suggesting Ukraine interfered in the 2016 election to help Democrats and Hillary Clinton's campaign.

Documents and testimony from more than a dozen witnesses eventually revealed that the July phone conversation was just one data point in a months-long effort by Trump and his allies, including his personal lawyer Rudy Giuliani, to leverage the weight of the US government and foreign policy to force Ukraine into acceding to his political demands.