Donald Trump’s second impeachment trial is getting under way as the defeated former president stands accused of inciting the deadly mob attack on the US Capitol.

Mr Trump’s lawyers are insisting as the Senate trial opens that he is not guilty of the sole charge of “incitement of insurrection” and that his fiery words were just a figure of speech as he encouraged a rally crowd to “fight like hell” for his presidency.

The Capitol siege on January 6 stunned the world as rioters stormed the building to try to stop the certification of then-president-elect Joe Biden’s victory. Five people were killed in the riot.

With senators gathered as the court of impeachment, the trial will begin with debate and then a vote on whether it is constitutionally permissible to prosecute the former president, an argument that could resonate with Republicans keen on voting to acquit Mr Trump without being seen as condoning his behaviour. They argue in filings the trial is “patently ridiculous”.

Prosecutors from the House of Representatives will cite the nation’s founders to declare a president “must answer comprehensively for his conduct in office from his first day in office through his last”.

There is no “January exception” just before he leaves office, they will argue, according to aides granted anonymity to discuss the arguments ahead of the trial.

“Sweeping it under the rug will not bring unity,” Senate majority leader Chuck Schumer said at the Capitol. “You need truth and accountability.”

It appears unlikely that the House prosecutors will call witnesses, in part because the senators sworn as jurors, forced to flee for safety, will be presented with graphic videos recorded that day. At his Mar-a-Lago club in Florida, Mr Trump has declined a request to give evidence.

The first president to face charges after leaving office and the first to be twice impeached for high crimes and misdemeanours while in office, Mr Trump remains a challenge to the nation’s civic norms and traditions even in defeat. Security remains extremely tight at the Capitol.

Acquittal is likely, but the trial will test the nation’s attitude towards his brand of presidential power, the Democrats’ resolve in pursuing him, and the loyalty of Mr Trump’s Republican allies defending him.

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

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

Mr Trump’s defenders are preparing to challenge both the constitutionality of the trial and any suggestion that he was to blame for the insurrection. They suggest that Mr 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 Mr Trump now that he has left office.

House impeachment managers, in their own filings, asserted that Mr Trump had “betrayed the American people” and 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.