HOW IT STARTS

The trial can’t begin until Speaker Nancy Pelosi names her team of “impeachment managers,” the band of lawmakers who will argue their case on the Senate floor. In 1999, the House appointed 13 managers, each responsible for a nuanced aspect of the factual and constitutional case against Clinton.

If Pelosi, who hasn’t said how many managers she’ll appoint, moves to formally name her team on Tuesday or Wednesday, the trial would begin this week. Look for House Intelligence Chairman Adam Schiff and House Judiciary Chairman Jerry Nadler, who led the impeachment inquiry, to be among the managers.

Senate rules require the chamber to receive the managers the day after they’re named, so the trial will begin quickly after Pelosi appoints them.

The oath (day 1): Once managers arrive at the Senate, they will read aloud the text of the articles of impeachment. The same day, Chief Justice John Roberts will be ushered into the chamber to preside over the trial. (Fun fact: Of the six senators who escorted Roberts’ predecessor William Rehnquist into the chamber, just one remains in the Senate: Patrick Leahy of Vermont.)

Roberts, whose job will be to enforce the rules of the Senate as well as the procedures that the chamber ultimately adopts, will be sworn in and then administer an oath to all 100 senators requiring them to "do impartial justice according to the Constitution and laws.”

In 1999, senators didn’t swear just once. After taking the oath collectively, they were called on to swear individually by the chief justice and then sign an “oath book.” Senators even suspended the chamber’s rules to allow a photograph to be taken of the members being sworn in.

The rules: Following the oath, McConnell will introduce a set of rules to govern the trial, including the length of arguments and when motions to dismiss the trial or hear from witnesses would be allowed. If there are any last-ditch efforts to end the trial before it begins, it'll be hashed out at this stage. McConnell has already signaled he plans to approve a rules package with only Republican votes over the objections of Minority Leader Chuck Schumer and Senate Democrats. Under the rules of the Clinton trial, the Senate met every day except Sunday. If Trump's trial looks similar, expect at least at least two weeks of argument, senator questioning and debate on calling witnesses.

Trial briefs (4-6 days): Get ready for a quick break. After adopting trial procedures in 1999, the Senate recessed for six days while the House and the president’s lawyers drafted formal trial briefs. Those briefs set out the arguments that will be presented over the ensuing days. In 1999, each side had five days to file briefs, and the House received an additional day to submit a reply to the president’s brief.

THE HEART OF THE TRIAL

Arguments (6 days): Here’s an area where McConnell has some wiggle room. In 1999, each side was granted 24 hours of floor time to make their arguments. Neither side approached their limit — even with 13 presenters on the House side. The House managers and White House lawyers at the time spread their arguments over three days. White House Counsel Pat Cipollone will likely lead Trump’s defense, and the president’s personal attorney Jay Sekulow is expected to have a prominent role on Trump’s legal defense team.

This phase of the trial is likely when House Democrats will have their best, and perhaps only, chance to make an uninterrupted case to Americans that Trump should be removed from office for seeking Ukraine’s intervention in the 2020 presidential race. Though Clinton’s trial extended well beyond opening statements, there’s a significant likelihood that Republican senators will seek ways to limit Democrats’ chances to present evidence for the remainder of the trial.

Questioning (3 days): Senators are not allowed to speak during the proceedings. But after each team presents its case, senators have an opportunity to question the lawyers by submitting their questions to the chief justice of the Supreme Court. In 1999, senators had 16 hours of floor time to ask questions, a process that took three full days. Republicans and Democrats alternated posing questions under a handshake agreement to attempt to keep the time equal. Groups of senators submitted their questions to Rehnquist, who posed them to the House or White House lawyers. Here, too, is an area where McConnell may have leeway to deviate from the Clinton procedures.

Off-ramps (3 days): This is the most crucial part of Trump’s trial — the source of the furor in recent weeks that led Pelosi to delay sending impeachment articles to the Senate. Once senators finish questioning the lawyers, they have the option to file a slew of trial motions — including a motion to dismiss the case and a motion to subpoena witnesses.

In 1999, Sen. Robert Byrd of West Virginia moved to dismiss the case against Clinton. Senators deliberated in closed session for four hours on the motion before adjourning without a vote. The next day, senators debated a motion to subpoena witnesses — and admit new evidence that hadn’t been available at the start of the trial. At the time, House impeachment managers asked to subpoena three witnesses and for the Senate to request trial testimony from Clinton himself. Only after both debates were done did the Senate reject the motion to dismiss and agree to the motion to call witnesses.

The most pressing question at this stage: Will the Senate defeat the motion to dismiss the case against Trump the way it did against Clinton in 1999? It would likely take just three senators to reject a dismissal, deadlocking the Senate in a 50-50 tie. But if a motion to dismiss passes, the trial will end without a vote on witness testimony. Trump said Sunday that he favors a dismissal, but he’s also called for voluminous witness testimony and has vacillated publicly on the issue.

Witnesses (0-7 days): In the Clinton trial, the Senate recessed proceedings for a week while witnesses were deposed in closed-door, videotaped sessions. Today, it’s unclear if there are enough Republican senators willing to demand the appearance of witnesses favored by House impeachment managers. A simple majority is needed, meaning four Republicans would have to join all Democrats. Bottom line for the trial: If you have 51 votes, you can do whatever you want.

It's also unclear if Trump will offer his own slate of witnesses, which would put Republicans seeking a quick trial in a difficult spot. Sen. Susan Collins, who is facing a tough re-election battle, revealed last week that she is working with a small group of Republican senators to ensure that both sides are able to call witnesses. Collins voted to acquit Clinton in 1999 and is perhaps the likeliest Republican who could vote to convict Trump.

Closing arguments (1 day): After dispensing with witnesses (or refusing to call them), the Senate will then take closing arguments from each side before deliberations.

HOW IT ENDS

Deliberations (1-3 days): In 1999, the Senate deliberated behind closed doors for three days, with each senator allowed to speak for 15 minutes. Though the sessions were private, each member had the option to put their remarks into the congressional record afterward.

The final vote (1 day): Clinton’s trial came to a close on Feb. 12, 1999, more than a month after it began. A similar trial for Trump, if it begins this week, would end on Feb. 21 — but could end much sooner if Senate Republicans take a different path.

WILDCARD: If the Senate trial starts this week, it’s all but guaranteed to be underway when a federal appeals court rules on Trump’s attempt to block former White House counsel Don McGahn from testifying to the House Judiciary Committee about his knowledge of potential obstruction of justice by Trump. Democrats have sought that ruling urgently and argued that it could become a factor in the impeachment trial if McGahn were made available prior to closing arguments.

Though the allegations against Trump are about his dealings with Ukraine, Democrats say McGahn’s testimony could point to a pattern of obstructive behavior and could even fuel additional articles of impeachment.

Clinton also delivered his State of the Union on Jan. 19, 1999 — the same day his lawyers began their three-day defense in the Senate. A protracted trial could conceivably put Trump in the same position when he delivers his address to Congress on Feb. 4.