Lawyers for Donald Trump have blasted the impeachment case against him as an act of "political theatre" and accused House Democrats on the eve of the former president's trial of exploiting the chaos and trauma of last month’s Capitol riot for their party's gain.

Trump's legal brief is a wide-ranging attack on the House case, foreshadowing the claims his lawyers intend to present on the same Senate floor that was invaded by rioters on January 6. 

The sharp-tongued tone, with accusations that Democrats are making "patently absurd" arguments and trying to "silence a political opponent," makes clear that Trump's lawyers are preparing to challenge both the constitutionality of the trial and any suggestion that he was to blame for the insurrection.

“While never willing to allow a ‘good crisis’ to go to waste, the Democratic leadership is incapable of understanding that not everything can always be blamed on their political adversaries, no matter how very badly they may wish to exploit any moment of uncertainty on the part of the American people," the defence lawyers say.

READ MORE:Key figures in Trump's Senate impeachment trial

'The most grievous constitutional crime ever'

In their brief, they suggest that Trump was simply exercising his First Amendment rights when he disputed the election results and argue that he explicitly encouraged his supporters to have a peaceful protest and therefore cannot be responsible for the actions of the rioters. 

They also say the Senate is not entitled to try Trump now that he has left office, an argument contested by even some conservative legal scholars, and they deny that the goal of the Democrats' case is justice.

House impeachment managers filed their own document on Monday, asserting that Trump had “betrayed the American people” and that there is no valid excuse or defence.

“His incitement of insurrection against the United States government, which disrupted the peaceful transfer of power, is the most grievous constitutional crime ever committed by a president," the Democrats said.

The trial will begin on Tuesday with a debate and vote on whether it's even constitutional to prosecute the former president, an argument that could resonate with Republicans keen on voting to acquit Trump without being seen as condoning his behaviour.

Opening arguments would begin on Wednesday at noon, with up to 16 hours per side for presentations.

Sabbath break

Under a draft agreement between Senate Majority Leader Chuck Schumer and Senate Republican Leader Mitch McConnell, the proceedings will break Friday evening for the Jewish Sabbath at the request of Trump's defence team and resume on Sunday.

There will likely be no witnesses, and the former president has declined a request to testify.

Trump is the first president to be twice impeached, and the only one to face trial after leaving the White House. 

The Democratic-led House approved a sole charge, “incitement of insurrection,” acting swiftly one week after the riot, the most violent attack on Congress in more than 200 years. 

Five people died, including a woman shot by police inside the building and a police officer who died of injuries the next day.

READ MORE:Trump impeachment goes to Senate, triggering trial over Capitol siege