WASHINGTON — Democrats' hopes of calling more witnesses in the impeachment trial of President Donald Trump appear to be on life support.

On Friday, Republican U.S. Sen. Lisa Murkowski of Alaska said she would vote against allowing new witnesses to be subpoenaed in the Senate, saying "the Congress has failed." Now, Ohio Sen. Rob Portman has also announced he will vote "no."

In a statement released shortly after Murkowski's remarks, Portman called President Trump's actions surrounding a potential quid pro quo with the President of Ukraine "wrong and inappropriate." However, the senator "[does] not believe that the president’s actions rise to the level of removing a duly-elected president from office and taking him off the ballot in the middle of an election."

Portman added, in part:

"Our country is already too deeply divided and we should be working to heal wounds, not create new ones. It is better to let the people decide. Early voting has already begun in some states in the presidential primaries. The American people will have the opportunity to have their say at the ballot box."

Rob Portman Trump
President Donald Trump greets Sen. Rob Portman, R-Ohio, and his wife Jane as he arrives at Lima Allen Airport to participate in a tour of Pratt Industries with Australian Prime Minister Scott Morrison, Sunday, Sept 22, 2019, in Lima, Ohio.
Evan Vucci/AP

Trump is accused of abuse of power and obstruction of Congress after being accused of withholding aid to Ukraine unless President Volodymyr Zelensky agreed to investigate former U.S. Vice President Joe Biden (one of the top contenders for the 2020 Democratic presidential nomination) and his son Hunter for "corruption." While Trump has denied any wrongdoing, critics say he was illegally trying to smear a political rival with the help of a foreign entity, and according to The New York Times former National Security Adviser John Bolton is alleging in a new book that Trump personally asked him to help pressure Ukraine into investigating the Bidens.

RELATED: President Trump says he gave aid to Ukraine after being asked by Sen. Rob Portman

Last month, Trump became just the third U.S. president in history to be impeached by the House of Representatives, and his trial began in the Senate last week. The latter chamber is controlled by a 53-47 Republican margin, meaning at least four GOP senators would have to vote in favor of allowing new witnesses such as Bolton during the trial. So far, only Susan Collins of Maine and Mitt Romney of Utah have flipped, meaning the motion is increasingly likely to be shot down and the trial could end with a probable Trump acquittal as soon as tonight.

It should be noted that the Trump administration blocked several key witnesses from testifying before the House, citing executive privilege. But Portman still placed most of the blame on his colleagues in the lower chamber, writing:

"Instead of using the tools available to compel the Administration to produce documents and witnesses, the House followed a self-imposed and entirely political deadline for voting on these articles of impeachment by Christmas, only to inexplicably stall for 28 days—time they could have used to subpoena witnesses and resolve privilege claims."

In order for Trump to be removed from office, 67 senators (two-thirds) must vote to convict him of at least one of the two counts. No president has ever been removed from office by the Congress, although President Richard Nixon faced certain impeachment and removal prior to his resignation in August of 1974.

WATCH LIVE: Watch live: Senators debate whether to call witnesses as trial end in sight

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