Here’s what to expect when President Trump’s historic impeachment trial begins in DC on Tuesday.

At 1 p.m., the US Senate will convene as a court of impeachment, and Senate Majority Leader Mitch McConnell will outline his rules for the trial.

The ensuing hearings are expected to consist of grueling 12-hour sessions each day. They will be held six days a week, from Monday to Saturday.

McConnell (R-Ky.) has repeatedly said he wants to put the kibosh on Democrats’ repeated demands for witnesses and bullishly suggested the trial may be over in as little as two weeks, just in time for Trump’s State of the Union address Feb. 4.

But Monday evening, Senate Minority Leader Chuck Schumer told reporters he would “force” a vote on the witnesses if McConnell didn’t include it in his rules — putting the screws to vulnerable GOP lawmakers who are facing tough re-election bids in November.

If witnesses are called, Trump’s impeachment trial may blow out to six weeks, White House officials said.

Senators are banned from talking and using cellphones during the proceedings. The strict policy will be a particular hardship for the four Democratic senators who are at the height of their presidential bids and staring down the Iowa caucuses and New Hampshire primary in coming weeks.

Some of McConnell’s rules are expected to follow those of former President Bill Clinton’s 1999 impeachment trial — giving the seven House Democratic impeachment “managers” the first stab at making their case, followed by a rebuttal from the White House defense team. Clinton’s trial lasted five weeks.

Sen. Ted Cruz (R-Texas) told Fox News on Friday that opening statements from both sides will consist of two 12-hour sessions.

After hearing arguments, the senators, acting as jurors, will have 16 hours to submit written questions to Supreme Court Chief Justice John Roberts, who is presiding over the hearing.

Roberts will pose the questions to the Democratic impeachment managers and White House counsel.

But before McConnell even gives his opening remarks, Democrats and Republicans are expected to battle over the central issue of introducing witnesses.

Schumer (D-NY) could introduce a motion for witnesses during the rules debate, while McConnell, as reported by Politico on Sunday, would prefer to have a vote on witnesses after each side presents its openings.

Schumer needs just four Republicans to flip and join Democrats in voting to subpoena potential key witnesses such as White House acting chief of staff Mick Mulvaney and former national security adviser John Bolton.

Sens. Susan Collins (R-Maine) and Lisa Murkowski (R-Alaska) have both suggested they would be open to hearing from witnesses after opening arguments.

Sen. Mitt Romney (R-Utah), a vocal critic of the president, has also said he would like to hear from witnesses, with one source telling The Post he was engaged in related discussions with Senate Democratic leadership.

Sen. Lamar Alexander (R-Tenn.), who is retiring at the end of this year, has also signaled he would be open to voting for witnesses, the Wall Street Journal reported.

A source in the Senate Democratic leadership on Monday suggested that more than four GOP lawmakers would vote with Democrats on the issue and added that Sen. Corey Gardner (R-Colo.) — considered the most vulnerable Republican senator in 2020 — was also “definitely” in play.

Gardner’s office could not immediately be reached for comment.

John Dowd, a lawyer who represented Trump during the special counsel Robert Mueller’s probe, which included an investigation into Russian meddling in the 2016 presidential election, said the addition of seasoned litigators Ken Starr and Alan Dershowitz to Trump’s legal team could ensure brevity in the proceedings because of their directness.

Even before the trial began, House Democrats and White House counsel filed scathing rebukes of each other’s arguments over the weekend — and Trump’s legal team Monday called for senators to “swiftly and roundly condemn” the articles of impeachment.