(Reuters) - The U.S. Senate expects to begin the trial of President Donald Trump in January if, as expected, the House of Representatives votes to impeach him this week.

FILE PHOTO: Chief Justice of the United States John G. Roberts is seen during a group portrait session for the new full court at the Supreme Court in Washington, U.S., November 30, 2018. REUTERS/Jim Young/File Photo

Here are the main players in what would be only the third such trial in U.S. history.

CHIEF JUSTICE JOHN ROBERTS

A conservative who was appointed by Republican President George W. Bush, Roberts might find himself celebrating his 65th birthday on Jan. 27 by presiding over Republican Trump’s impeachment trial.

Under the U.S. Constitution, the chief justice of the highest court is the referee in presidential impeachment trials.

Senate Majority Leader Mitch McConnell has noted that if Roberts presides in a similar fashion to then-Chief Justice William Rehnquist in the trial of President Bill Clinton, he could allow any disagreements over procedures to be worked out by the senators themselves, probably through one or more Senate floor votes.

But Roberts has been known to surprise court-watchers. For example, early this year he joined liberals in a 5-4 abortion case decision and did the same in a 2012 ruling upholding a central feature of Democratic former President Barack Obama’s signature healthcare law.

SENATORS MITCH MCCONNELL AND CHUCK SCHUMER

The Senate majority and minority leaders, respectively, will be tasked with trying to reach a bipartisan deal over the rules governing any Trump trial.

McConnell has raised the possibility of a trial that could consist only of arguments by House Democrats for conviction and by White House lawyers for acquittal, with no witnesses testifying.

Schumer has called for a full and open trial, while McConnell has said there is no chance that Trump will be convicted by fellow Republicans.

Both Senate leaders will be keenly aware that the trial will be taking place just as the 2020 election campaign begins to speed up. McConnell will be anxious not to allow the trial to turn into a circus while Schumer will be hoping that some moderate Republicans split away and vote to convict Trump just as he campaigns for re-election.

TRUMP’S LEGAL TEAM

Much like a trial held in the U.S. judicial system, the accused - in this case Trump - would be defended by a team of lawyers arguing for his acquittal.

The White House has not yet announced who would spearhead this effort on the Senate floor.

White House counsel Pat Cipollone is expected to play a leading role, an administration official told Reuters. He has been working with deputies Patrick Philbin and Michael Purpura.

Cipollone, a 53-year-old Republican, sent an eight-page letter to Congress in October laying out why the White House was refusing to cooperate with the House inquiry, calling it a “charade.”

Trump lawyers are likely to argue that there is no evidence that the president did anything wrong and that the House investigation was partisan and flawed.

HOUSE ‘MANAGERS’

House Speaker Nancy Pelosi has not yet named the Democratic “managers” who would prosecute the case against Trump in the Senate. But some obvious potential choices would be House Judiciary Committee Chairman Jerrold Nadler and House Intelligence Committee Chairman Adam Schiff. They have been spearheading the impeachment effort in the House since Pelosi announced the start of a formal inquiry on Sept. 24.

Pelosi likely would weigh several factors in choosing the managers, including their expertise on constitutional law and familiarity with details of the Trump impeachment case, as well as their oratorical eloquence.