Washington, DC - The United States House of Representatives is set to vote on Wednesday to send two articles of impeachment against President Donald Trump to the Senate for trial.

Earlier on Wednesday, House Speaker Nancy Pelosi named seven Democrats to serve as House managers, or prosecutors, in the trial. They include: Adam Schiff, Jerrold Nadler, Zoe Lofgren, Hakeem Jeffries, Val Demings, Jason Crow and Sylvia Garcia.

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"We are going to keep the focus on the stunning, corrupt abuse of power engaged in by Donald Trump," said Jeffries, chair of the House Democratic Caucus.

The action sets into motion parliamentary formalities over the next several days, with a Senate trial expected to begin on January 21 and run for at least three weeks, Senate leaders said on Tuesday.

The Democratic-led House on December 18 impeached Trump for abuse of power over his efforts to get Ukraine to launch an investigation into his political rival, Joe Biden, and obstruction of Congress for refusing to cooperate with the House impeachment investigation. Trump has denied any wrongdoing, labelling the impeachment as a "hoax" and "witch-hunt".

Pelosi wields the Speaker's gavel as she presides over the final of two House of Representatives votes approving two counts of impeachment against Trump [Jonathan Ernst/Reuters]

House Speaker Nancy Pelosi delayed sending the articles of impeachment to try and pressure Senate Republicans to ensure that there was a fair trial in the Senate. But after Senate Majority Leader Mitch McConnell said earlier this month Republicans had the votes to move forward with a trial, Pelosi announced the articles would be sent.

Senate trial

Trump is almost certain to be acquitted in the Republican-controlled Senate, where leaders have disparaged the House impeachment as a flawed attempt to damage the president ahead of the US election in November.

"This is the most rushed, most biased, and most partisan impeachment process in history," said Senator John Thune, the Republican Whip.

"We were told at the outset, as the House was rushing through this, that there was a real sense of urgency, that they had to get this done," Thune told reporters. "Clearly after the Speaker now having sat on it for over a month, it's clear that all along this has been a partisan exercise on the part of the Democrats and an attempt to overturn a presidential election."

The trial is expected to move forward with opening statements before a decision on whether witnesses will be allowed is made.

There is a small group of Senate Republicans - including Senators Susan Collins, Lisa Murkowski and Mitt Romney - who have indicated they may join with Democrats to call new witnesses and testimony in the Senate trial. The Democrats just need four Republicans to join them in calling witnesses.

Witnesses?

Democrats want the Senate to call acting Chief of Staff Mick Mulvaney and former National Security Adviser John Bolton to testify. Bolton, who refused to appear before House investigators, has said he is willing to testify to the Senate if subpoenaed.

Bolton had direct Oval Office conversations with Trump about Ukraine. He called the pressure campaign on Ukraine "a drug deal" that he refused to be part of as national security adviser, according to testimony in the House.

Former National Security Adviser John Bolton gestures while speaking at the Center for Strategic and International Studies [File: Pablo Martinez Monsivais/AP Photo]

McConnell reaffirmed on Tuesday he has sufficient Republican votes to pass an organising resolution in the Senate that would define how the trial will be conducted.

According to McConnell, the plan would allow House managers and the president's defence lawyers to put forth their respective cases, before a formal question-and-answer session.

"That would set up the arguments by the parties, the prosecutors and the defence, and then the written question period, and then after that, the more contentious issue of witnesses would be addressed by the Senate," McConnell said.

Some Republicans have suggested they would want to call former Vice President Biden and his son as witnesses. Democrats will argue there is no evidence the Bidens did anything wrong.

"We will just have to wait and see what the feeling of the Senate is after listening to the arguments and the period of written questions," McConnell said.

McConnell said there was not sufficient support among Republicans to simply dismiss the House's articles of impeachment, an outcome Trump's lawyers were seeking.

"We want to make sure all the president's rights are protected in the process the Senate is considering adopting," said Eric Ueland, the director of White House legislative affairs.

"As far as we understand it, the president's rights are protected, including the potentiality of a motion to dismiss," Ueland told reporters.