The ongoing Senate impeachment trial could end as soon as this evening after key Republicans — particularly Sen. Lamar Alexander — have voiced their intent to vote against subpoenaing further witnesses.

Sen. Marsha Blackburn has also voiced her intent to vote against calling additional witnesses, likely leaving Democrats without enough votes in the Senate to continue the trial.

Beginning on Jan. 16, the Senate impeachment trial came to be after the House of Representatives adopted articles of impeachment last year on Dec. 19, alleging charges against President Donald Trump of obstruction and abuse of power.

Those charges stemmed from a May 25 phone call between Trump and Ukranian President Volodymyr Zelensky, where Trump had allegedly leveraged his power as president to coerce Zelensky to investigate his domestic political opponent, Joe Biden.

Now on its 16th day, the Senate impeachment trial will hear closing arguments Friday afternoon and evening, with senators voting on whether to call additional witnesses — a vote that will certainly fail after Alexander’s statement late Thursday night.

“There is no need for more evidence to prove that the president asked Ukraine to investigate Joe Biden and his son, Hunter; he said this on television on October 3, 2019, and during his July 25, 2019, telephone call with the president of Ukraine,” Alexander said. “There is no need for more evidence to conclude that the president withheld United States aid, at least in part, to pressure Ukraine to investigate the Bidens; the House managers have proved this with what they call a ‘mountain of overwhelming evidence.’ There is no need to consider further the frivolous second article of impeachment that would remove the president for asserting his constitutional prerogative to protect confidential conversations with his close advisers.”

Despite voicing his intent to not support the calling of additional witnesses, Alexander conceded that Trump’s behavior was “inappropriate.”

“It was inappropriate for the president to ask a foreign leader to investigate his political opponent and to withhold United States aid to encourage that investigation,” Alexander said. “When elected officials inappropriately interfere with such investigations, it undermines the principle of equal justice under the law. But the Constitution does not give the Senate the power to remove the president from office and ban him from this year’s ballot simply for actions that are inappropriate.”

Alexander’s intent to vote against supporting additional witnesses is seen by many as the last shot the Democratic caucus had at extending the trial, as he was often considered a swing vote. Republican Senators Susan Collins of Maine, Mitt Romney of Utah and Lisa Murkowski of Alaska have all previously signaled they were open to supporting the calling of more witnesses, but for the vote to pass, four Republican senators would be required to vote alongside Democrats.

“The question then is not whether the president did it, but whether the United States Senate or the American people should decide what to do about what he did. I believe that the Constitution provides that the people should make that decision in the presidential election that begins in Iowa on Monday.”

In a statement made Friday morning, Blackburn also voiced her intent to vote against the calling of additional witnesses, and has remained consistent in her belief that the impeachment inquiry was "politically driven."

“I am a no vote on additional witnesses — we’ve had the testimony of 17 people,” Blackburn said. “The House said that their case was iron-clad, that they had overwhelming evidence, and now they’re saying, ‘oh wait, but more.’ It is not the responsibility of the U.S. Senate to give the House an impeachment do-over. They are to do the investigating, and they are to establish the impeachment articles, send them to us, and we take an action on the impeachment.”