Republican Sen. Mitt Romney invited the wrath of his own party on Wednesday when he made the shocking announcement that he would vote to convict President Donald Trump of abuse of power following his impeachment trial.

Trump's eldest son, Donald Trump Jr., said Romney was now "officially a member of the resistance" and "should be expelled" from the Republican Party.

Ronna McDaniel, the chairwoman of the party and Romney's niece, also voiced her disapproval. "This is not the first time I've disagreed with Mitt, and I imagine it will not be the last," she said.

"Wrong, wrong, wrong move," said GOP Rep. Jim Jordan, one of Trump's biggest attack dogs in Congress.

Speaking on the Senate floor ahead of a final vote on whether to convict or acquit Trump, Romney said he expected to face backlash from his colleagues.

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On Wednesday, Sen. Mitt Romney of Utah made history by becoming the first 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 chamber was expected to vote to acquit Trump of two articles of impeachment: abuse of his office and obstruction of 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 has firmly supported Trump and is helping to fund his reelection 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. "I, along with the GOP, stand with President Trump."

A press release from the Republican Party following Romney's announcement was titled "Mitt Romney turns his back on Utah."

Here's how key Republican figures reacted:

Trump's son, Donald Trump Jr., suggested the Republican caucus should expel Romney.

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

Newt Gingrich, the former House speaker, skewered Romney and pointed to comments he made in 1994 criticizing former President Ronald Reagan.

Republican congressman Lee Zeldin said Romney voted to convict Trump because he "absolutely despises" the president.

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

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

Trump was impeached in December. Both articles of impeachment related to his efforts to strong-arm Ukraine into interfering in the 2020 election while he withheld $391 million in vital military aid and dangled 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 inquiry by investigating a bogus conspiracy theory suggesting Ukraine interfered in the 2016 election to help Democrats and Hillary Clinton's campaign.