WASHINGTON (AP) — The Senate launched Donald Trump’s historic second impeachment trial today, with lawyers for the former president insisting he is not guilty of inciting mob violence at the Capitol to overturn the election while prosecutors say he must be convicted of the “most grievous constitutional crime” even though he’s gone from the White House.

Trump faces a sole charge of incitement to insurrection over the Jan. 6 Capitol siege, an attack that stunned the nation and the world after he encouraged a rally crowd to “fight like hell” for his presidency. Rioters stormed the building trying to stop the certification of President-elect Joe Biden’s victory.

No witnesses are expected to be called, in part because the senators sworn as jurors will be presented with graphic videos of the scenes they witnessed that day, forced to flee for safety. Under COVID-19 protocols senators will distance for the trial, some even using the visitors’ galleries. Holed up at his Mar-a-Lago club in Florida, Trump has declined a request to testify.

The first president to face charges after leaving office and the first to be twice impeached for high crimes and misdemeanors, Trump continues to challenge the nation’s civic norms and traditions even in defeat. Security remains extremely tight at the Capitol. While acquittal is likely, the trial will test the nation’s attitude toward his brand of presidential power, the Democrats’ resolve in pursuing him and the loyalty of Trump’s Republican allies defending him.

“In trying to make sense of a second Trump trial, the public should keep in mind that Donald Trump was the first president ever to refuse to accept his defeat,” said Timothy Naftali, a clinical associate professor at New York University and an expert on Richard Nixon’s impeachment saga.

“This trial is one way of having that difficult national conversation about the difference between dissent and insurrection,” he said.

White House press secretary Jen Psaki said Monday that Biden will be busy with the business of the presidency and won’t spend much time watching the televised proceedings. “He’ll leave it to his former colleagues in the Senate,” she said.

In filings Monday, lawyers for the former president lobbed a wide-ranging attack against the House case, dismissing the trial as “political theater” on the same Senate floor that was invaded by the mob.

Trump’s defenders are preparing to challenge both the constitutionality of the trial and any suggestion he was to blame for the insurrection. They suggest Trump was simply exercising his First Amendment rights when he encouraged his supporters to protest at the Capitol, and they argue the Senate is not entitled to try Trump now that he has left office.

House impeachment managers filed their own document Monday, asserting Trump had “betrayed the American people” and has no valid excuse or defense.

The trial will begin today with a debate and vote on whether it’s constitutionally permissible to prosecute the former president, an argument that could resonate with Republicans keen on voting to acquit Trump without being seen as condoning his behavior.

Under an agreement between Senate Majority Leader Chuck Schumer and Republican leader Mitch McConnell, the opening arguments would begin at noon Wednesday, with up to 16 hours per side.