Impeachment managers will continue to make their case US President Donald Trump improperly interfered in Congress' probe of his dealings with Ukraine in their final day of arguments on Friday. Watch the Senate proceedings streaming live here at 1 p.m. ET.

Democratic managers from the House of Representatives will try to convince senators and the US public that the Republican president is guilty of the charge of obstructing Congress for withholding key witnesses and documents from the investigation.

Related: Impeachment trial in the Senate — what’s happening?

The House impeached Trump last month on that charge and a separate charge of abuse of power for allegedly trying to coerce Ukraine’s government into digging up dirt on former Vice President Joe Biden, a top contender for the 2020 Democratic presidential nomination.

The impeachment trial in the Senate, the third such proceeding in US history, will determine whether Trump is ousted from power less than 10 months before he faces re-election.

The US Constitution sets out the impeachment process for removing a president who commits "high crimes and misdemeanors." Trump denies wrongdoing, while his Republican allies argue his conduct does not rise to the level of an impeachable offense.

Related: Is Trump a better friend to Ukraine than Obama was?

Once Democrats conclude their opening arguments, Trump's legal team will have up to 24 hours over three days to mount a defense. A two-thirds vote of the chamber is required to eject Trump from office.

Trump on Friday retweeted dozens of supporters who repeated his criticism of the proceedings as unfair and politically motivated. The former reality television personality also complained his lawyers would have to begin arguments on Saturday, when, he said, nobody watches television.

"Looks like my lawyers will be forced to start on Saturday, which is called Death Valley in T.V.," Trump wrote on Twitter.   

As the trial neared the end of its first week, there was little sign that Senate Republicans were being persuaded by the Democratic case.

Democrats spent Thursday meticulously detailing their allegations that Trump only grew interested in corruption in Ukraine when it appeared that Biden could become a serious political threat.

Democratic Representative Adam Schiff, the lead House manager, said Trump had used US foreign policy for his own personal interest, and that failing to oust him from office would open the door to a "lot of damage" in the coming months.

"This is why if you find him guilty, you must find that he should be removed. Because right matters. Because right matters and truth matters. Otherwise we are lost," Schiff said in his closing argument on Thursday.

In a July 25 phone call, Trump pressed Ukrainian President Volodymyr Zelenskiy to investigate Biden and his son Hunter, who served on the board of Ukrainian energy company Burisma. Trump temporarily withheld $391 million in US military aid to Ukraine, which Democrats say was leverage for his demands.

Democrats push for witnesses

On Friday, the impeachment managers will argue that Trump also unlawfully refused to cooperate with the House probe of the matter by directing officials to ignore Democratic requests to testify and for relevant documents.

Key administration officials who refused to comply with subpoenas in the probe included Vice President Mike Pence, White House acting Chief of Staff Mick Mulvaney and Secretary of State Mike Pompeo. Former national security adviser John Bolton refused a request by the House to testify.

Democrats sought to have Bolton testify in the trial, but senators voted along party lines on Tuesday against all Democrats' proposed witnesses.

During the proceedings, Democrats have argued the Senate should allow new witnesses such as Bolton to testify. Republicans have resisted their push but have threatened to call a witness such as Joe or Hunter Biden in retaliation.

The Senate could return next week to that issue. Democrats are holding out hope that they can persuade enough moderate Republican senators to vote to allow additional witness testimony and documents into the trial.

Democratic Representative Val Demings, one of the House impeachment managers, said Democrats will continue to press for that, but added there was a strong case against the president without additional testimony.

"The best witness is the president himself and listening to his own words" in the Zelenskiy call and Trump's public calls for other nations to interfere in the November election, Demings said in an interview with MSNBC. "That's hard to ignore."

By David Morgan and Richard Cowan/Reuters

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