LIVE: Senate reconvenes for Trump's impeachment trial after key GOP senator announces she will vote against calling new witnesses

Andrew Harnik/AP

• The Senate reconvened Friday to debate whether to call additional witnesses forward in President Donald Trump's impeachment trial.
• House impeachment managers have been pushing hard to call new witnesses, like former national security adviser John Bolton, who could share firsthand knowledge of Trump's pressure campaign in Ukraine that hasn't yet come to light.
• Friday's proceedings come after The New York Times reported on yet another bombshell claim from Bolton's upcoming book, in which Bolton says Trump personally directed him to pressure Ukraine to cave to his political demands.
• Shortly before the trial, a key Republican senator, Lisa Murkowski, announced she will vote against calling new witnesses, dealing a final blow to the push to call witnesses.
• Scroll down to watch the trial and follow Insider's live coverage.
• Visit Business Insider's homepage for more stories.

The Senate reconvened on Friday to debate whether to call new witnesses forward in President Donald Trump's impeachment trial. After the debate, there will be a vote on witnesses and bringing forward new evidence, but it's unclear how long Friday's session will last and how long the debate will be.

Friday's proceedings also come after The New York Times reported on another bombshell claim from former national security adviser John 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.

The House Intelligence Committee, which spearheaded the impeachment inquiry, heard from 17 witnesses who testified to Trump's efforts to bully Ukraine into acceding to his personal demands. But House managers are pressing the Senate to call additional witnesses, like Bolton, who can provide firsthand knowledge of Trump's pressure campaign.

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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Here are the 4 witnesses Democrats want to call and why each one is relevant

• Former national security adviser John Bolton
  • Bolton is a key figure in several events at the center of Trump's impeachment. He was at a July 10 meeting during which Gordon Sondland, the US's ambassador to the EU, pushed Ukrainian officials to deliver the political investigations Trump wanted in exchange for a White House meeting for Zelensky.
  • Bolton will reportedly reveal in his upcoming book that Trump directly told him he would withhold Ukraine's aid until the country gave in to his demands for investigations.
  • The former national security adviser also claims Trump asked him during a meeting in May to call Zelensky and push him to meet with Giuliani, who was spearheading Trump's pressure campaign.
• Acting White House chief of staff Mick Mulvaney
  • Bolton claims Mulvaney was present at the May meeting in which Trump asked him to call Zelensky.
  • Mulvaney is also the head of the Office of Management and Budget, which took on a lead role in carrying out Trump's order to freeze Ukraine's aid. Emails and other documents also indicate that Mulvaney was in the loop on Trump's decision to withhold Ukraine's military aid from the start.
  • Mulvaney publicly acknowledged last year that part of the reason the White House froze the security assistance was because Trump wanted Zelensky to investigate a conspiracy theory about Ukrainian election interference that targets the Democratic Party.
• Robert Blair, an aide to Mulvaney
  • Blair has direct knowledge of Mulvaney's involvement in the Ukraine pressure campaign.
  • The New York Times reported that early on as Trump debated withholding aid, Blair wrote to Mulvaney in an email that the administration should "expect Congress to become unhinged" if the White House tried to pull back spending that was approved in Congress.
• Michael Duffey, an OMB official
  • Duffey officially ordered the freeze in Ukraine's aid 91 minutes after Trump's phone call with Zelensky on July 25.
  • Duffey wrote that based on "guidance" he had gotten and in "light of the Administration's plan to review assistance to Ukraine … please hold off on any additional DoD obligations of these funds, pending director from that process."

House impeachment managers dig in on calling witnesses after Murkowski deals a fatal blow to the motion

House manager Val Demings displayed the graphic above as she emphasized that the Senate had called witnesses in every one of the 15 previous impeachment trials in US history.

Murkowski explains her decision to vote against calling witnesses: 'Given the partisan nature of this impeachment from the very beginning and throughout, I have come to the conclusion that there will be no fair trial in the Senate'

Here's her statement:

"I worked for a fair, honest, and transparent process, modeled after the Clinton trial, to provide ample time for both sides to present their cases, ask thoughtful questions, and determine whether we need more.

"The House chose to send articles of impeachment that are rushed and flawed. I carefully considered the need for additional witnesses and documents, to cure the shortcomings of its process, but ultimately decided that I will vote against considering motions to subpoena.

"Given the partisan nature of this impeachment from the very beginning and throughout, I have come to the conclusion that there will be no fair trial in the Senate. I don't believe the continuation of this process will change anything. It is sad for me to admit that, as an institution, the Congress has failed. 

"It has also become clear some of my colleagues intend to further politicize this process, and drag the Supreme Court into the fray, while attacking the Chief Justice. I will not stand for nor support that effort. We have already degraded this institution for partisan political benefit, and I will not enable those who wish to pull down another.

"We are sadly at a low point of division in this country."

See Also:

• Trump's lead attorney in the impeachment trial could also be a witness, according to Bolton's book
• GOP Sen. Lamar Alexander called Trump's actions 'inappropriate' but says he will vote against a motion for witnesses in impeachment trial
• Top House Democrat said John Bolton 'strongly implied that something improper' happened with former ambassador Marie Yovanovitch's ouster