The Senate voted against calling witnesses in Trump's impeachment trial, which is a first in US history

• The Senate on Friday voted against calling witnesses in President Donald Trump's historic impeachment trial.
• The motion to call witnesses failed, with 51 senators voting against it and 49 voting in favor.
• Democrats repeatedly made the case that former national security adviser John Bolton should be called to testify.
• Witnesses were called in all 15 impeachment trials in the Senate in US history.
• Visit Business Insider's homepage for more stories.

The Senate on Friday voted against calling witnesses in President Donald Trump's impeachment trial.

The motion for witnesses failed, with 51 senators voting against the measure and 49 voting in favor of it.

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 needed 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 voted for additional witnesses.

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 would also vote against calling more witnesses.

The highly anticipated vote came after a fierce debate over whether to call witnesses on Friday.

The seven Democratic House impeachment managers, who act as prosecutors in the trial, argued that the Senate has a duty to call additional witnesses, like former national security adviser John Bolton, who have firsthand evidence of Trump's alleged misconduct.

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.

Calls for Bolton to testify intensified after the New York Times reported that the former national security adviser wrote in a forthcoming book that the president personally told him he would not release Ukraine's military aid until the country publicly committed to pursuing the investigations Trump wanted.

Earlier Friday, The Times revealed in another report that Bolton also claims Trump asked him during a meeting last May to call Zelensky and ensure he met with Rudy Giuliani, Trump's personal lawyer, when Giuliani planned to travel to Ukraine that month.

Witnesses were called in all of the 15 impeachment trials in the Senate prior to Trump's, including the trials for the only other presidents who were impeached - Andrew Johnson and Bill Clinton.

Democrats essentially accused Trump or trying to blackmail a foreign country with congressionally-approved military funds into launching probes that would've aided his 2020 reelection campaign.

The impeachment proceedings spiraled out of a whistleblower complaint that centered on a July 25 phone call between Trump and Ukrainian President Volodymyr Zelensky.

During the call, Trump urged Zelensky to launch inquiries into former Vice President Joe Biden and his son, Hunter Biden, as well as a debunked conspiracy theory that Ukraine, not Russia, interfered in the 2016 election.

Biden is a leading contender for the 2020 Democratic nomination, and there's no evidence of wrongdoing or illegal activity on his or Hunter's part in Ukraine.

The effort to urge Ukraine to launch these investigations went well beyond the July 25 call, and raised the alarm among many career diplomats and officials - in some cases leading to resignations. Trump's personal lawyer, Rudy Giuliani, was central to these efforts.

The frozen security assistance was eventually released to Ukraine in early September - less than a week after three House committees launched investigations into Trump's dealings.

Meanwhile, Trump has maintained he did nothing wrong, and is expected to be acquitted in the GOP-controlled Senate.