This has been updated with the latest news.

For every Senate impeachment trial, the senators currently serving are the ones who decide how the trial will work. There are rules from the 1980s about how to run a Senate trial, but they’re intentionally vague on some really important things, such as what kind of evidence can be shared and how long a trial should be.

So Senate Majority Leader Mitch McConnell (R-Ky.) introduced his proposal Monday for his optimal trial: short and quick. Democrats oppose it for a couple reasons, and with push back from a swing Republican vote on impeachment, Sen. Susan Collins (Maine), McConnell loosened some of the restrictions on evidence and arguments, report The Post’s Seung Min Kim and Elise Viebeck.

Here is how the trial will work under the current rules McConnell is proposing, and where Democrats object to them:

After a debate on the rules Tuesday, opening arguments start Wednesday

It means senators are spending the expected start date of opening arguments, Tuesday, arguing and voting on the parameters of the trial — parameters that Senate Democrats did not see until Monday, either.

(By comparison, the Bill Clinton impeachment trial was seen as a good-faith effort on the part of the Senate Republican majority and Democratic minority to compromise on a fair trial.)

The setup of Trump’s trial came together somewhat hurriedly after House Speaker Nancy Pelosi (D-Calif.) held back the articles of impeachment for three weeks in an attempt to shape this trial.

During Tuesday’s vote, Senate Minority Leader Charles E. Schumer (D-N.Y.) could force the Senate to vote on whether senators want to hear from witnesses now, as opposed to later in the trial as McConnell’s resolution calls for.

McConnell is trying to avoid having to call witnesses for various reasons that largely boil down to protecting Trump. We can expect a witness vote on Tuesday to fail, even though there may be a majority of senators who support witnesses later in the trial. McConnell has kept his Senate Republicans in line to avoid having that debate at the outset.

Another contention point was that senators would have to vote on whether to allow evidence House Democrats uncovered in their months-long impeachment investigation to be introduced to senators. But from pushback from Collins, McConnell changed this rule to allow evidence to be admitted unless a senator objects.

During the Clinton trial, each side printed out pages and pages of evidence and had it sitting on senators’ desks before the start of the trial, without depending on Senate approval of such action. It’s not likely that a majority of senators object to seeing the evidence, but Democrats say the fact they have to take this extra step to vote on it is indicative of how Senate Republicans don’t want to hold a balanced trial.

Each side will now have three days to present their cases

The original proposal called for smashing 24 hours of argument allotted it to both sides into two days, which would have meant Democrats making their case past on the East coast. But after pushback from Collins, that time limit has now been stretched to three days, meaning the trial likely won’t go as late — and the senators themselves, forced to surrender their phones and sit in their chairs silently for the duration — won’t be quite as tired.

McConnell has said he is working “in total coordination” with the White House defense team, so we can assume that Trump’s defense didn’t have a problem with the time crunch it will be under. In a legal brief filed Monday, the defense team urged senators to “immediately” acquit Trump.

Why the rush? Well, in addition to political incentives for Republicans to end this dramatic trial for Trump, it’s running up against a number of big political moments on the 2020 calendar, including Trump’s State of the Union address.

The busiest season of the 2020 political calendar

After opening arguments, senators will have 16 hours to ask questions in writing

This is consistent with the Clinton trial, where senators asked more than 100 questions. The “in writing” part is in line with the official Senate rules for an impeachment trial, designed to prevent grandstanding by lawmakers (some of whom are running for president, while others have competitive reelection bids in November). Chief Justice John G. Roberts Jr. will read the questions out loud, and the appropriate side, defense or prosecution, can answer them.

The vote to call witnesses comes after all this

It’s a make-or-break point for the trial. After a four-hour debate on this issue, four Republican senators will need to cross party lines and vote with Democrats to keep the trial going and call new witnesses.

If that happens, the Senate would be introducing new evidence that House Democrats could not get access to because Trump prohibited his current and former aides from cooperating with House impeachment investigators. But if the Senate approves witnesses, Trump’s defense could also call its own, and some Senate Republicans have pushed the idea of voting for witnesses to force Hunter Biden and the whistleblower to testify.

McConnell has not said this outright, but he is probably banking on Republican senators wanting to end the trial at this point and just vote on whether to acquit or convict the president on each article of impeachment. This vote could come a week or two into the trial, which will have been going on six days a week and sometimes late into the night. Senators cannot do any other legislative business during the hours the trial is going on.

Senate Democrats object to having such a vote so late in the trial for that reason. Even though this vote was also delayed during the Clinton impeachment trial, they point out that it was less consequential. Republicans controlled the impeachment process in the House and Senate, and there was a separate grand jury investigation that thoroughly interviewed key people, so there weren’t any new witnesses to uncover.

The Senate could still vote to subpoena witnesses. Romney has said he will vote in support of having former national security adviser John Bolton testify. Sen. Susan Collins (R-Maine) has been very open to having witnesses, as has Sen. Lisa Murkowski (R-Alaska). Democrats need just one more Republican senator to join them to keep the trial going.

At any point, Trump’s defense team can propose dismissing the trial entirely without a vote on whether to acquit or convict him. In the lead-up to the trial, that is something Trump was urging senators to do, but Senate Republicans have pushed back on that, arguing that a trial with a vote to acquit him after hearing evidence is better for clearing his name — and more palatable to American voters.

Closing arguments, deliberations and a vote to acquit or convict Trump

After the defense and prosecution present their cases and senators ask questions — or after witnesses testify, if the Senate approves that — both sides will present their final arguments, much like closing arguments in a trial.

All of this is being done in the open, but during the Clinton trial, the Senate voted to deliberate behind closed doors and took several days. McConnell’s resolution is less clear on how the Senate will deliberate before the final votes.

Once senators are done debating, they will hold two votes on each article of impeachment. Senators will be voting on whether to convict the president of each article. If he is convicted of even one, he would be thrown out of office. Or they can vote to acquit, which would allow him to stay in office with his name cleared.

It would take a separate, simple-majority vote to prevent him from running for office again.