US President Donald Trump holds up a newspaper with the headline "Acquitted" as he arrives to speak at the 68th annual National Prayer Breakfast on Thursday in Washington, DC. Trump said Thursday that he suffered a "terrible ordeal" during his impeachment. Photo: AFP

On the eve of US former president Donald Trump's impeachment trial, his legal team Monday denounced the case as unconstitutional, calling it "absurd" to hold the former president responsible for the deadly riot at the US Capitol.

But in a preview of their prosecuting arguments, Democrats accused Trump of committing the "most grievous constitutional crime" in the 232-year history of the American presidency by inciting his supporters to storm Congress on January 6.

The House of Representatives impeached Trump for a historic second time in January over his role in the deadly siege, and his trial - the first of a former president - begins Tuesday with the Senate's 100 members sitting as jurors.

The chamber's leaders announced that they and the legal teams had reached agreement on the rules of the process, which was expected to launch Tuesday at 1 pm with debate and a vote on the constitutionality of the trial itself.

Arguments were expected to be heard from Wednesday, with each side provided 16 hours over two days.

Trump is a deeply damaged political figure but remains a powerful force in the Republican Party.

Charged with "incitement of insurrection," he is likely once again to avoid conviction due to loyal support in the Senate, but his lawyers contended in their final pre-trial filing that the Constitution does not give the chamber jurisdiction to try a former president.

"The Senate should dismiss these charges and acquit the president because this is clearly not what the framers wanted or what the Constitution allows," his attorneys Bruce Castor, David Schoen and Michael T. van der Veen wrote.

"Indulging House Democrats hunger for this political theater is a danger to our Republic democracy and the rights that we hold dear."

The defense used blunt language in their 78-page brief, saying it was "simply absurd" to argue that Trump conjured up a mob to commit violent crime, and that those who attacked the Capitol did so on their own.

The lawyers rejected as "patently ridiculous" the trial of a former president, a private citizen who cannot be removed "from an office that he no longer holds."

President Joe Biden, who succeeded Trump on January 20, weighed in Monday but declined to address whether Trump should be found guilty or denied the right to hold political office in the future.

"We'll let the Senate work that out," Biden said.

White House spokeswoman Jen Psaki later told reporters that Biden ran against Trump in 2020 "because he felt he was unfit for office."

"But he's going to leave it to the Senate to see this impeachment proceeding through," Psaki added.

AFP