The United States House of Representatives on Wednesday formally handed off two articles of impeachment against President Donald Trump to the Senate, clearing the way for a trial.

The House of Representatives impeached Trump on December 18 for abuse of power related to his efforts to get Ukraine to launch an investigation into his political rival, former Vice President Joe Biden, and obstruction of Congress for his refusal to participate in the impeachment inquiry. Trump has denied any wrongdoing.

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House Sergeant at Arms Paul Irving and Clerk of the House Cheryl Johnson deliver the Articles of Impeachment against President Donald Trump to Secretary of the Senate Julie Adams on Capitol Hill in Washington, January 15, 2020 [Jose Luis Magana/Reuters]

Trump is almost certain to be acquitted in the Republican-led Senate, but the trial could deliver some unexpected moments if witnesses are called.

As the Senate prepares for the trial, here's a look at what happens next.

When will the trial take place? What time?

Senate Majority Leader Mitch McConnell said on the trial would start "in earnest" on Tuesday following procedural matters scheduled to be completed this week.

In terms of timing, most expect the trial to go six days a week (Monday-Saturday) and begin at 1pm local time (18:00 GMT).

What will happen first?

Following a host of formalities, including the swearing-in of members and other housekeeping matters, the Senate will put forth an initial resolution outlining how the chamber will move forward with the trial.

According to McConnell, that measure would set up a phase for arguments by the House managers, who act as prosecutors, and Trump's defence team. There would then be a period for senators to submit written questions, which would be answered out loud by managers and lawyers in the Senate chamber. This phase could last one to two weeks.

US Speaker of the House Nancy Pelosi signs the Articles of Impeachment against US President Donald Trump [Brendan Smialowski/AFP]

McConnell only needs 51 votes to approve these rules. The Republicans hold a 53-47 majority. Unlike the impeachment trial of former President Bill Clinton, support for the Trump trial rules package will likely fall along party lines.

The Senate must also formally notify Trump of the impeachment articles and ask for his reply.

What about witnesses?

The partisan divide on the rules is largely due to the question of witnesses. Democrats want to call at least four witnesses, including acting White House Chief of Staff Mick Mulvaney and former White House National Security Adviser John Bolton.

Most Republicans say that calling witnesses will only draw out the inevitable: an acquittal. There are some cracks within the Republican caucus, however, and Democrats are hard at work trying to lobby those Republicans to support a motion to call witnesses.

Some Republicans have also said they may want to call Biden and his son, Hunter, as witnesses.

How long will the trial last?

If witnesses are called, the trial could last well into February. The first voting of the 2020 Democratic presidential election takes place on February 3 in Iowa. Four senators - Bernie Sanders, Elizabeth Warren, Amy Klobuchar and Michael Bennet - who are also vying for the Democratic presidential nomination will be off the campaign trail during the trial itself as attendance is mandatory.

Trump is also scheduled to deliver his State of the Union address on February 4 (Clinton gave his State of the Union speech while on trial in 1999).

Who presides over the trial?

According to the Constitution, the chief justice of the Supreme Court presides over the trial. The current Supreme Court chief justice is John Roberts.

In his annual report at the end 2019, Roberts said: "As the New Year begins, and we turn to the tasks before us, we should each resolve to do our best to maintain the public's trust that we are faithfully discharging our solemn obligation to equal justice under law."

Who are the House managers?

The House has named seven managers, who will serve as prosecutors in the trial. They are:

Adam Schiff Jerrold Nadler Zoe Lofgren Hakeem Jeffries Val Demings Jason Crow Sylvia Garcia

House Managers walk to the US Senate to deliver the Articles of Impeachment against US President Donald Trump on Capitol Hill [Jim Watson/AFP]

Read more about the managers here.

Who is on Trump's defence team?

Trump is still in the process of finalising his defence team, but White House counsel Pat Cipollone will lead the group. The team will also include White House Counsel Jay Sekulow. Cipollone and Sekulow are expected to make the opening arguments before the Senate.

The team also is expected to include Pat Philbin and Mike Purpura, who are deputies of Cipollone.