Donald Trump's impeachment trial begins with harrowing Capitol riot video

Trump was impeached by the Democratic-led House of Representatives last month for his role in the January 6 attack on the Capitol by a mob of his supporters

US senators viewed harrowing video from the storming of Congress by Donald Trump's supporters at the start of his historic second impeachment trial Tuesday, despite the defence team's attempt to declare the whole procedure unconstitutional.

According to Trump's lawyers, a president cannot be tried after impeachment when he has already left office.

Democratic impeachment managers -- lawmakers in the role of prosecutors -- attacked the unconstitutionality argument, saying that Trump had broken his oath in a naked bid to retain power after losing the November election.

Refusing to accept defeat to Joe Biden, Trump spread lies about vote-rigging and repeatedly pressured officials, including then vice president Mike Pence, to try and stop the transfer of power.

Read | As Trump's impeachment trial opens, evidence mounts Capitol attack was planned

Finally, on January 6, Trump told enraged Republican supporters near the White House to "fight like hell." The crowd, chanting "stop the steal," then attacked Congress, where Pence and lawmakers were in the process of certifying Biden's victory.

"If Congress were to just stand completely aside in the face of such an extraordinary crime against the Republic, it would invite future presidents to use their power without any fear of accountability," Democratic prosecutor Joe Neguse said.

Video from the January 6 mayhem played back inside the ornate Senate packed the biggest punch.

Senators -- who witnessed the events first hand when they had to be rushed to safety that day -- watched raw footage of Trump's speech and the crowd's ensuing assault on the Capitol.

The video montage showed the mob chanting pro-Trump slogans as it smashed through the doors, swarmed over police, and managed for the first time in history to disrupt the congressional vote certifying the election.

Read | Impeachment case against Trump based on 'cold, hard facts': Prosecutor

"If that's not an impeachable offence, then there is no such thing," impeachment manager Jamie Raskin said.

Fighting tears, Raskin recounted how he and his family -- who were visiting to watch the certification -- had been trapped, listening to "the sound of pounding on the door like a battering ram, the most haunting sound I have ever heard."

"This cannot be the future of America," he implored senators.

Trump is the first president ever to face two impeachment trials -- he was already acquitted in 2020 of abuse of office -- as well as the first in history to be tried after leaving the White House.

His team is basing its case largely on the procedural argument that a former president cannot be tried, calling the Senate trial "absurd."

They also argue that whatever Trump said during his January 6 rally is protected by the constitutional right to free speech and did not amount to ordering the assault on Congress.

Also Read | Trump's impeachment trial starts, constitutional challenge in spotlight

The trial is clearly uncomfortable for many Republican senators, who, like their Democratic colleagues, had to flee to safety during the violence. Reminders of the mayhem are everywhere around them, with thousands of National Guard troops still deployed around the newly fortified Capitol building.

Despite this, a second acquittal is all but certain for Trump, who is holed up in his luxury Mar-a-Lago resort in Florida.

Democrats hold 50 of the 100 Senate seats and Vice President Kamala Harris is able to cast a tie-breaking vote. But it would take a two-thirds majority for a conviction, meaning at least 17 Republican senators would have to join.

Amped up on four years of Trump's populist claims to be fighting for ordinary people against the elites, huge numbers of Republican voters continue to support the ex-president, pushing their party ever further to the right.

Polls show that a small majority of the country overall believes Trump deserves conviction. An Ipsos/ABC News poll found 56 per cent back this, while a Gallup poll found 52 per cent support.

Among Republicans, however, an overwhelming majority opposes convicting Trump.

It's not clear yet how long the trial will last but it will be shorter than the three-week marathon of Trump's first impeachment and could end as soon as next week.

Biden, who succeeded Trump on January 20, is attempting to stay above the fray.

Daily, the White House is sending a message that the Democrat is focused instead on the fragile economy and the desperate effort to vaccinate Americans against the still out-of-control Covid-19 pandemic.

White House Press Secretary Jen Psaki reiterated Tuesday that Biden is "going to wait for the Senate to determine the outcome of this."

"He's not going to comment on the back and forth arguments, nor is he watching them," Psaki told reporters.

If Trump were convicted, the Senate would then hold a simple-majority vote on barring him from future public office.

But even if the impeachment trial ends in acquittal, calls to punish Trump for his behavior will likely continue, including possibly a push for a bipartisan vote of censure.