Washington, DC - US President Donald Trump's Republican allies in a sharply divided United States Senate on Wednesday are poised to acquit the president on two articles of impeachment put forward by the Democrat-controlled House of Representatives.

The vote, scheduled for 4pm (21:00GMT), follows nearly two weeks of often lengthy Senate sessions as senators considered the charges of abuse of power over Trump's dealings with Ukraine and obstruction of Congress for refusing to participate in the House impeachment inquiry.

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It will cap off the drama that has consumed Washington since the House announced its impeachment inquiry in September.

Senate Republicans view the House impeachment of Trump as a partisan drive to damage Trump ahead of his re-election campaign and many adopted the posture that charges against him were not proven beyond a reasonable doubt.

Senate Republican leader Mitch McConnell said Democrats wanted to impeach Trump from the moment he ran for office.

"It insults the intelligence of the American people to pretend this was a solemn process reluctantly begun because of withheld foreign aid," McConnell said.

"Washington Democrats think President Donald Trump committed a high crime or misdemeanour the moment he defeated Hillary Clinton in the 2016 election," McConnell said in Senate floor remarks on Tuesday.

"That is the original sin of this presidency," McConnell said.

In this image from video, House impeachment manager Representative Adam Schiff speaks during closing arguments in the impeachment trial of Trump [Senate TV/AP Photo]

Democrats view Trump's impeachment as a way to put evidence of his misconduct on the record for the American people to see.

They accuse him of abusing his power of office by orchestrating a power campaign to get Ukraine to announce investigations into his political rivals. Trump has denied any wrongdoing.

While acquittal was always the likely outcome, the question of whether the Senate would call witnesses came to a dramatic head last week amid new revelations from former White House National Security Advisor John Bolton about Trump's alleged wrongdoing. After four hours of arguments, the Senate voted to block witnesses and new evidence in a 51-49 vote.

"This is the first impeachment trial of a president or an impeachment trial of anybody else, that was completed with no witnesses and no documents," Senate Democratic leader Chuck Schumer said.

Democrats wanted the Senate to call Bolton and other witnesses the White House blocked from testifying during the House impeachment inquiry.

"Republicans refused to get the evidence because they were afraid of what it would show," Schumer said in Senate floor remarks on Tuesday. "It fails the laugh test. It makes people believe - correctly in my judgment - that the administration and top Republicans are all hiding the truth."

Some Republicans likened Trump's conduct more to "maladministration", a lower, non-impeachable standard set aside by the 18th Century writers of the US Constitution.

"I do not believe the facts in this case rose to the high bar the founders set for removal from office," said Republican Senator John Thune.

In this image from video, White House counsel Pat Cipollone speaks during the impeachment trial of Trump [Senate TV/AP Photo]

It would take a two-thirds vote, or 67 senators to vote to remove Trump from office. Republicans control a 53-47 majority in Congress's upper chamber, meaning it would take 20 Republicans to break party ranks to convict Trump, never a likely outcome.

With only nine months to go until the next US presidential election, Republicans said preventing Trump from standing for re-election would wrongly short-circuit the US democratic process.

Two remaining political issues in Wednesday's vote are: whether some Democrats might join Republicans in voting to acquit and whether some Republicans may give speeches against the president's conduct.