President Trump's impeachment team wasn't expecting Senator Mitt Romney's guilty vote on one of the two articles of impeachment against the president, a senior source on the team confirmed to CBS News. Romney was the only Republican to break with his party Wednesday and vote guilty, on the first article of impeachment — the one charging abuse of power.

As recently as Tuesday, Romney had informed Mr. Trump's allies he was going to vote along with his Republican colleagues. The Romney vote deprived the president of the unanimity he strongly desired from his party in the impeachment vote.

One Trump adviser told CBS News the team viewed it as an "opportunistic" move by Romney.

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It was the first time a senator had ever voted to convict a president of his own party.

The lone defection on one of the articles wasn't nearly enough to change the trial's outcome, which was never in much doubt. A guilty verdict for either article would have required 20 Republican senators to vote to convict the president. He was acquitted by the Senate on both articles. The other charged obstruction of Congress.

Mr. Trump watched the final Senate votes on the articles from the private dining room on the side of the Oval Office with some of his top aides, a senior White House official confirmed to CBS News.

Many of the president's top players in the impeachment trial, including family members and senior members of his legal team, held a private party Wednesday night at the Trump International Hotel in Washington to celebrate the acquittal.

Mr. Trump's son, Donald Trump Jr., and son-in-law, Jared Kushner attended, along with White House counsels Pat Cipollone and Jay Sekulow. Top White House aides Kellyanne Conway and Hogan Gidley were there. Also spotted were members of Mr. Trump's House impeachment team including GOP Representatives Doug Collins, Lee Zeldin, Jim Jordan, John Ratcliffe and Mark Meadows.

Mr. Trump didn't go due to a previously scheduled private dinner in the White House residence, according to Conway. She said it wasn't associated with the events of the day.

At one point, Trump Jr. was asked what he thought of the trial results but his only response was to say it was "good to see" the reporter before leaving the hotel with his security entourage.

The party was primarily for the impeachment team. Several other members of Trump world, including senior campaign officials, were seen in the hotel lobby bar but weren't invited to the private part of the hotel, called "The Townhouse," where the main event was being held.