What do you think? Leave a respectful comment.

Chief Justice of the United States John Roberts arrives to preside over the Senate impeachment trial of President Donald T...

The impeachment trial rules are set. Here’s what happens next

The Senate approved ground rules for President Donald Trump’s impeachment trial that include unexpected concessions addressing some of the Democrats’ concerns about the process. But Republicans did not budge on Democrats’ resolution amendments that would commit to witness testimony and subpoenas for documents (as opposed to waiting until after opening arguments). The resolution passed 53-47 along party lines early Wednesday morning after more than 12 hours of tense debate between the House managers and Trump’s legal team.

Following weeks of back and forth between Democrats and Republicans, Senate Majority Leader Mitch McConnell on Tuesday abruptly backed away from two key pieces of his proposed resolution released Monday night.

One change redistributes the total number of hours that House managers and Trump’s defense team will have for opening arguments — instead of two days, they will each present for the same amount of time over three days. Another change allows evidence gathered in the House impeachment inquiry to be included in the record.

On Tuesday, Senate Minority Leader Chuck Schumer introduced several amendments related to subpoenas, only to have them tabled on party-line votes. Schumer said these rules will result in a rushed trial.

The foundation for these procedural rules dates back to the 1868 impeachment trial for former President Andrew Johnson. The rules were most recently updated in 1986, and then used in the 1999 trial for former President Bill Clinton, as well as a number of federal judges who faced impeachment.

Here’s how the trial process will work.

How is the trial structured?

Based on the rules approved Wednesday, both sides — the House Democratic managers and the White House defense team — will have 24 hours, divided over three days, to present their opening arguments before the Senate. U.S. Chief Justice John Roberts is presiding over the trial.

House Democrats will go first, starting Wednesday. They previewed their argument and laid out the articles of impeachment in a brief released Saturday, saying that Trump abused his power by withholding a White House visit and military aid from Ukraine in exchange for the announcement of investigations into former Vice President Joe Biden and his son, Hunter.

Democrats also said the president obstructed the House impeachment inquiry by defying congressional subpoenas for testimony and relevant documents. The seven-member manager team, led by House Intelligence Chairman Adam Schiff, D-Calif, summarized their case Tuesday during the debate over the rules for the trial.

After the House managers conclude, Trump’s legal defense team will make their opening presentation. In a brief released Monday, Trump’s team did not deny the president pressured Ukraine, but argued he had legitimate reasons for seeking an investigation into the Bidens and withholding the aid. Trump’s team also described the articles of impeachment as a “brazenly political act” and claimed it was unconstitutional.

Trump’s defense team includes White House counsel Pat Cipollone, the president’s personal attorney Jay Sekulow, and Kenneth Starr, the independent counsel whose investigation of former President Bill Clinton in the 1990s led to his impeachment. In remarks on the Senate floor Tuesday, Cipollone defended the trial format and urged Democrats not to delay the proceedings. “It’s time to start this trial. It’s a fair process,” he said.

READ MORE: PBS NewsHour’s guide to the impeachment proceedings

Can senators participate in the trial?

Procedure prevents senators from speaking while both sides make their case. Once that phase is over, however, senators may submit questions in writing for Roberts to read aloud to the managers and Trump’s defense team. This questioning period can last up to 16 hours, according to the rules.

After the question period concludes, the House managers and Trump’s defense team will next have two hours apiece for additional arguments or to address senators’ questions. The Senate then moves to a debate over whether to subpoena witnesses or new evidence.

What power does Chief Justice Roberts have?

Senate procedure states that the presiding officer — Roberts in this case — may “rule on all questions of evidence including, but not limited to, questions of relevancy, materiality, and redundancy of evidence and incidental questions.”

The chief justice is mainly a figurehead for impeachment trial proceedings, but senators are expected to direct questions or motions to Roberts rather than interrupting proceedings. Roberts could attempt to exert more authority by ruling on requests for witness testimony and other evidence.

However, a senator who disagrees with a ruling from Roberts can put the issue up for the full Senate vote, in which case Roberts’ decision could be overruled.

WATCH LIVE: Trump’s impeachment trial in the Senate

What happens if the Senate votes to hear witnesses?

This phase of the trial is still up in the air. Fifty-one senators would need to approve a measure calling for witnesses in the trial — meaning at least four Republicans and all 45 Democratic lawmakers and two independents who caucus with the Democrats would have to vote yes. It remains unclear if enough Republicans would buck the GOP leadership and join Democrats on the measure.

Under the trial rules, the Senate will consider the issue of witnesses after opening presentations, following the precedent set in the Clinton impeachment trial. Also like Clinton’s trial, the rules require that potential witnesses first give depositions. McConnell’s organizing measure defers to the 1986 guidance for how the rest of the trial should be handled.

Potential trial witnesses could include former national security adviser John Bolton, who refused to testify in the House but has since said he would testify before the Senate if subpoenaed. Democrats have also said they want to hear from Mick Mulvaney, the acting White House chief of staff, and Michael Duffey, a top official for the Office of Management and Budget. For their part, Trump and some Republicans have also called for testimony from Biden and Schiff.

If witnesses were allowed in the trial, they could be questioned by the House managers and Trump’s legal team.

After hearing from witnesses and evaluating any new evidence — or if the Senate rejects calls for witnesses and new evidence — the House managers and Trump’s defense will then give closing arguments. After that, the Senate has the option to hold a closed-door debate over the articles of impeachment. In Clinton’s case, each senator spoke for 15 minutes.

Finally, the senators would vote on whether to remove Trump from office. Removal requires a two-thirds majority of the senators present at the proceedings. If all senators are present, this means 20 Republicans would have to vote in favor of removal — an improbable outcome.