The Senate reconvened Friday to debate whether to call additional witnesses forward in President Donald Trump's impeachment trial.

After several hours of debate, the Senate blocked a measure to call new witnesses, with 49 senators voting for it and 51 against.

The schedule for the rest of Trump's impeachment trial is now up in the air as the Senate figures out how to "land the plane," according to one Republican senator.

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The Senate on Friday officially blocked a measure to call additional witnesses in President Donald Trump's impeachment trial.

The move came after a contentious debate during which House impeachment managers argued that the Senate has a duty to hear testimony from firsthand witnesses, like former national security adviser John Bolton, who can provide new evidence in Trump's trial.

The president's lawyers, meanwhile, argued that the Senate already has enough information from the 17 witnesses who testified in the House's impeachment inquiry.

Friday's proceedings came after The New York Times reported on another bombshell claim from Bolton's upcoming book, in which Bolton claims Trump personally asked him to help pressure Ukraine to cave to his personal demands.

The House of Representatives impeached Trump last month for abuse of power and obstruction of Congress. The two articles of impeachment relate to the president's efforts to strong-arm Ukraine to deliver politically motivated investigations targeting his rivals.

While doing so, Trump withheld $391 million in military aid to Ukraine and dangled a White House meeting that Ukrainian President Volodymyr Zelensky desperately sought and still hasn't gotten.

Fifty-one senators need to vote in favor of calling witnesses for the motion to pass. There are currently 45 Democrats, two independents who caucus with Democrats, and 53 Republicans in the Senate.

That means four Republican senators need to side with the Democratic caucus for the Senate to call witnesses.

In the Republican caucus, only Sens. Mitt Romney of Utah and Susan Collins of Maine have publicly indicated they would vote in favor of calling witnesses to testify.

Sen. Lamar Alexander of Tennessee, once considered a possible pro-witness Republican, announced Thursday night that he would not vote in favor of witnesses.

Sen. Lisa Murkowski of Alaska, another closely-watched potential swing vote on the matter, confirmed Friday afternoon that she will also vote against calling more witnesses.

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