President Donald Trump speaks during the White House Summit on Child Care and Paid Leave in the South Court Auditorium on the White House complex, Thursday, Dec. 12, 2019, in Washington. Credit: Evan Vucci | AP

WASHINGTON – If the House impeaches President Donald Trump, that will only mean we have completed the first half of the process to remove a president from office. What comes next is a Senate trial to decide whether, based on the House’s impeachment recommendation, senators should vote to convict the president, ending his tenure and possibly preventing him from running again.

There are rules from the 1980s about how to run a Senate trial, but they’re intentionally vague on the really important things: what kind of evidence can be shared, how long it should be, and how the defense and prosecution should present their cases.

When Senate Majority Leader Mitch McConnell, R-Kentucky, and Minority Leader Chuck Schumer, D-New York, get together to decide those rules, we’ll walk you through how a Senate trial will work.

Until then, here’s what we know about a Senate impeachment trial – and what we don’t.

What we know:

— The timing is specific: A trial has to begin shortly after the House impeaches the president. Here’s what that looks like with the Christmas break, according to McConnell on the Senate floor Wednesday: “Assuming that House Democrats send us articles of impeachment next week, a Senate trial will have to be our first item of business in January.”

It also has to be six days a week, for at least part of the day, and senators can’t do any legislative business in the hours the trial is going on. But there are no rules about how long it has to go every day, nor how many weeks it has to last.

There are no rules about how to present evidence. That will be determined for this specific trial beforehand by Senate Republicans and Democrats. McConnell says those negotiations may come next week. But once everyone is seated for the trial, the roles for key players are set. Such as:

— The chief justice of the United States, John G. Roberts Jr., will preside: For impeachment trials of judges, the vice president presides, but the rules assume the vice president would be biased on impeachment of the president. We’ll get more into Roberts’s role in the “what we don’t know” section.

— Trump can appoint his counsel: It’s generally understood they need to be personal, not White House lawyers. They can give opening and closing statements and question any witnesses.

— House Democrats can do the same: They are called impeachment managers. The House will select lawmakers who will be the prosecution, examining and cross-examining witnesses as Trump’s lawyers can.

— This is not exactly like a criminal trial: For example, senators are both the judge and the jury. (They can even be called as witnesses!)

— Senators can ask questions of witnesses in writing only: Which Roberts will read out loud.

— This has to be done in the open: Especially the vote. The only time senators can go behind closed doors is to deliberate, says Josh Chafetz, a constitutional expert at Cornell Law School, though senators during the impeachment trial of President Bill Clinton did spend a good chunk of it deliberating in private. Senators don’t have to be there to vote, either, and any absences would lower the two-thirds majority it takes to convict Trump. But Chafetz had a hard time seeing any lawmakers getting away with skipping such a consequential vote.

— There is precedent for bipartisan cooperation: It may surprise you to know that the Clinton impeachment trial was celebrated as civil and bipartisan. Former Senate historian Donald Ritchie: “The Senate went out of its way to write rules that would be fair to both sides and to conduct itself in a dignified manner.” In fact, the top Republican and top Democratic senators got a standing ovation from all other senators after the trial was done “for averting the bitter partisanship that consumed the House during its impeachment debate,” The Post reported at the time.

The history of impeachment (of presidents or judges) suggests what happens in the House influences Trump’s fate in the Senate: “Whenever there’s been a bipartisan vote in the House, there has been a substantial bipartisan vote in the Senate on impeachment. Every time there has been a party-line vote in the House, there has been a substantial party-line vote in the Senate,” Ritchie said.

What we don’t know:

— Who will be called as witnesses, whether the Senate can subpoena people and whether the Senate will take new evidence: The Senate doesn’t even have to call witnesses, which is something McConnell is seriously considering. Also, whether the Senate will interview witnesses on the floor in real time, or form a committee and interview and film them, airing the video on the Senate floor, is not known. (In the Clinton trial, they had Monica Lewinsky testify via previously videotaped interviews, and Chafetz said they decided against allowing new witness testimony.) Senators have to figure out these details before the trial gets started.

— How partisan this will be: Trump wants it to be uber-partisan, to have House Intelligence Committee Chairman Adam Schiff, D-California, and the whistleblower testify. There’s even some talk among his Senate allies of folding in former vice president Joe Biden’s son Hunter Biden.

Some Republicans have pushed back on that. It will ultimately be up to McConnell, in consultation with the rest of the Senate, to decide how to shape this.

He’s given no indication he’s leaning toward a super-partisan trial, and we can be sure he is aware of his role in history helping shape it. “He’s an institutionalist,” said Sarah Burns, a constitutional law expert at Rochester Institute of Technology, “and he does care about the legacy under his watch. It’s also true that he has occasionally, very subtly – perhaps too subtly for Trump to understand – said, ‘This is your mess, and I’m not going to be dragged down by you.’ So I do think that he’ll be inclined to make this a fairly calm and not circusy trial.”

For example, Trump’s personal lawyer Rudolph W. Giuliani said ahead of the trial that he wants to report to Senate Republicans what he found recently in Ukraine on a supposed fact-finding mission about the Biden family. No Senate Republican is taking him up on that offer that we know of, and as Trump urges Hunter Biden to testify, McConnell is considering limiting the time frame of the trial and not having any witnesses.

— How Roberts will handle his role as overseer: McConnell doesn’t have to just get a majority of senators on board with what he wants to do. He has to get it by Roberts, who will be ruling on whether anything senators want to do, such as admitting evidence, fits within their predetermined rules. (A supermajority could overrule Roberts, but Burns says there’s also a complicated parliamentarian maneuver where a simple majority could overrule Roberts’s interpretation of the rules. Republicans only have a three-vote majority over Democrats, so they don’t have a ton of wiggle room to drastically change the rules once they’re set.)

— Roberts can do battle with the Senate on his interpretation of the rules, or he can largely defer to them. Supreme Court watcher Russell Wheeler says he thinks Roberts will lean toward deference. The chief justice overseeing the Clinton trial, William H. Rehnquist, said proudly when it was all over: “I did nothing, and I did it particularly well.” And Rehnquist’s assistant during that trial is now a close aide to Roberts.

“As chief justice, he does want to protect the court,” Wheeler said. “He doesn’t want the court to get involved in sideshows about whether his actions in the impeachment trial shed light or had influence about the decisions he makes as a justice on Supreme Court cases.”