House prosecutors who argued for Donald Trump’s conviction of inciting the US Capitol riot say they proved their case despite the “heartbreaking” verdict and have railed against the Senate’s top Republican “for trying to have it both ways” in acquitting the former president.

A day after Mr Trump was acquitted at his second Senate impeachment trial in two years, bipartisan support appeared to grow in the US for an independent September 11-style commission to make sure such a horrific assault could never happen again.

The end of the quick trial on Saturday hardly put to rest the debate about Mr Trump’s culpability for the January 6 insurrection as the political fallout unfolded.

More investigations into the riot are already planned, including Senate hearings scheduled for February and a House review of Capitol security.

On Sunday (local time), lawmakers from both parties signalled even more inquiries were likely.

“There should be a complete investigation about what happened,” said Senator Bill Cassidy, one of seven Republicans who voted to convict Mr Trump.

Senator Cassidy said that as Americans heard all the facts, “more folks will move to where I was”. He was censured by his state’s party after the vote, which was 57-43 to convict but 10 votes short of the two-thirds required.

A close Trump ally, Senator Lindsey Graham, said he looked forward to campaigning with Mr Trump in the 2022 election. But, he acknowledged Mr Trump had some culpability for the siege that killed five people and disrupted certification of Democrat Joe Biden’s White House victory.

“His behaviour after the election was over the top,” Senator Graham said.

“We need a 9/11 commission to find out what happened and make sure it never happens again.”

The Senate acquitted Mr Trump of inciting an insurrection after House prosecutors argued he unleashed a mob by stoking a months-long campaign of spreading debunked conspiracy theories that the 2020 election was stolen from him.

Mr Trump’s lawyers argued his words were not intended to incite the violence and the trial was intended to prevent him serving in office again.

The conviction tally was the most bipartisan in American history but left Mr Trump to declare victory and signal a political revival.

Several House impeachment managers criticised Minority Leader Mitch McConnell, who voted to acquit Mr Trump. After the vote, Mr McConnell said the former president was “practically and morally responsible for provoking the events of that day” but the Senate’s hands were tied because he had left office.

“It was powerful to hear the 57 guilties and then it was puzzling to hear and see Mitch McConnell stand and say not guilty and then minutes later stand again and say he was guilty of everything,” Representative Madeleine Dean said.

“History will remember that statement of speaking out of two sides of his mouth.”

Ms Dean backed the idea of an impartial investigative commission “not guided by politics but filled with people who would stand up to the courage of their conviction”.

The lead House impeachment manager, Representative Jamie Raskin, called the trial a “dramatic success in historical terms” by winning unprecedented support from Republican senators. He said the verdict did not match the strength of the evidence.

Fellow House prosecutor Stacey Plaskett described the verdict as “heartbreaking” but “the founders knew what they were doing and so we live with the system that we have”.

-AAP