The president has called it “a charade”.
His lawyers have termed it part of a broader “illegitimate partisan effort to take him down” by Democrats.
But whether he likes it or not, Donald Trump has been impeached by the House of Representatives, and the “trial” of those articles is about to be heard in the Senate.
Much of what will play out over the coming days and even weeks, remains unclear.
Late on Monday, on the very eve of the start of proceedings, the Republican leader in the Senate, Mitch McConnell, issued a set of rules which he said will govern how the proceedings take place. Yet even at this stage, as many things are fluid as they are fixed in stone.
What will happen on Tuesday January 21?
The impeachment process trial resumes at 1pm EST (6pm GMT) on Tuesday. It is likely that very soon after it convenes, the chamber will be asked to vote on a resolution to govern the proceedings. Late on Monday, Mr McConnell proposed a condensed, two-day calendar for each side to give opening arguments. It also pushes off any votes on witnesses until later in the process, rather than up front, as Democrats demanded.
According to Mr McConnell, after the four days of opening arguments – two days per side – senators will be allowed up to 16 hours for questions to the prosecution and defence, followed by four hours of debate.
Will there be any witnesses?
Democrats have been pushing to be permitted to call several witnesses, among them former and serving White House officials, to give evidence. While some Republicans in the Senate have not ruled out supporting such a move, it has now become clear a decision regarding those witnesses will not be decided on Tuesday unless Democrats are some how able to force the issue. On Monday the Democratic leader in the Senate, Chuck Schumer, termed the Republican plan a “cover-up”.
When will the prosecution and defence be heard?
Once the rules have been adopted, Democratic House “managers” who form the prosecution team will begin to present their case against the president. It is unclear whether that will start on Tuesday or the next day. One report said the first evidence would likely be aired on Wednesday. When the House managers have finished, the president’s team will respond with its opening arguments.
Could the White House seek to have the two articles dismissed?
Reuters quoted a senior aide to the Republican leadership as saying lawyers for Mr Trump could move early in the proceedings to ask senators to dismiss all charges. It said such a motion that would likely fall short of the support needed to succeed.
So what about witnesses such as John Bolton?
CNN pointed out Mr Connell’s resolution also said after presentations from the impeachment managers and the president’s legal team and then 16 hours of questions from senators, the Senate will consider “the question of whether it shall be in order to consider and debate under the impeachment rules any motion to subpoena witnesses or documents”.
When will the senators actually vote?
It had been expected that because of the ongoing wrangling, no such vote would take place before the end of January or beginning of February. If Mr McConnell gets his way, that process could be quicker than anticipated.
Are any Republicans likely to vote to impeach Trump?
At this point, no. In the unlikely event the Senate voted to impeach the president, he would be replaced by Mike Pence.
What else is on the president’s agenda?
On 4 February, a day after Democrats hold their first primary ballot of the 2020 political cycle in Iowa, Mr Trump is scheduled to deliver the annual State of the Union address to a joint session of Congress.
How does all of this impact the president’s re-election chances?
Assuming he is cleared by the Senate, the president will continue to portray himself as a victim of Democrats’ ill intentions. It will likely harden support among his base. What remains unclear is whether it helps earn him new supporters. Most likely, by November 2020 so many other things will have played out that impeachment is far from the minds of most voters.
Additional reporting by agencies