Sen. Lamar Alexander, R-Tenn., arrives in the Capitol for a vote on Wednesday, Dec. 11, 2019. | Photo By Bill Clark/CQ-Roll Call, Inc via Getty Images

Alexander made his announcement late Thursday — effectively deciding the outcome of a vote on witnesses.

Sen. Lamar Alexander (R-TN), a closely watched swing vote on the question of whether to call witnesses in the Senate impeachment trial, has made up his mind.

After some deliberation, Alexander announced Thursday that he would vote against calling witnesses, dealing a major blow to Democrats who have pushed for additional testimony from individuals with direct knowledge about the White House’s handling of aid to Ukraine.

Alexander elaborated on his decision in a 15-tweet statement. “There is no need for more evidence to prove something that has already been proven and that does not meet the US Constitution’s high bar for an impeachable offense,” he wrote.

Alexander, in his posts, appeared to point to the argument made by Trump counsel Alan Dershowitz, who’s said the quid pro quo the president has been charged with committing — even if true — did not rise to the level of an impeachable offense.

In several tweets, he acknowledged that President Donald Trump did condition aid to Ukraine in exchange for political investigations. This charge, though, was not an impeachable one, Alexander concluded.

Alexander, a moderate from Tennessee who’s retiring this year, was seen as a strong target for Senate Democrats to recruit to their side because he wasn’t facing the same electoral pressure as other lawmakers.

Along with Sens. Mitt Romney, Susan Collins and Lisa Murkowski, Alexander was one of a handful of lawmakers considered potential swing votes on the witness question. As of Thursday evening, Romney and Collins had both indicated that they were in favor of calling witnesses, while Murkowski had yet to signal a clear stance.

“I am going to go reflect on what I have heard, re-read my notes and decide whether I need to hear more,” Murkowski told reporters Thursday.

Alexander announced a vote in line with that of most Republicans, many of whom have expressed disinterest in calling more witnesses. And at this point, the witness question that has been dogging the rest of the trial is effectively settled.

Without Alexander, Democrats don’t have the pivotal fourth vote they need to reach a 51-vote simple majority that’s required to approve motions for witnesses. Even if Murkowski were to vote in favor of witnesses, there would be a tie, and it’s likely Chief Justice John Roberts will elect not to break the tie, resulting in the motion ultimately failing.

This means these Senate proceedings will be the first presidential impeachment trial in US history that does not include witness testimony.

What comes next

The official vote on whether to allow witnesses is still slated to take place on Friday, after closing arguments from the House impeachment managers and Trump’s legal defense team.

Now that it seems that the Senate won’t be calling witnesses, the trial is set to move quickly toward an acquittal vote that could take place late Friday evening. Republicans have been eager to wrap the trial this week, and they’re poised to acquit Trump of both articles of impeachment.

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