Democrat momentum behind the second impeachment of Donald Trump has gained senior Republican support.
Senator Pat Toomey said he believed the president had committed “impeachable offences” and that his role in the deadly Capitol riots by a violent mob of his supporters needed thorough investigation.
Mr Toomey also called for Mr Trump‘s resignation – the second Republican to do so since Wednesday’s violence.
Donald Trump’s opponents in Boston promote impeachment against the US president
His comments came as investigators attempting to find out the identities of all those who stormed the building revealed that some off-duty police officers and firefighters may have been among them.
Police departments in Virginia and Washington state have placed officers on leave, while they examine whether they took part in unlawful acts while away from work.
And fire departments in Florida and New York City have reported to federal authorities allegations that some of their members may also have been present.
Five people, including a Capitol police officer, died when the protesters broke into the building as Congress met to certify the results of the presidential election.
The crowd surged to the domed symbol of American democracy following a rally near the White House, where the outgoing president repeated his false and unproven claims that the election was stolen from him – and urged his supporters to march in force toward the Capitol.
This is what has enraged even previously loyal Republicans like Mr Toomey – and fuelled momentum behind a bid to impeach the president for what would be an unprecedented second time.
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Officer crushed in door as mob storm Capitol
There are now 200 co-sponsors for the impeachment legislation that Democratic representative Ted Lieu plans to introduce on Monday.
But while Mr Toomey called for the president to step down, he stopped short of saying whether he would vote to remove him from office at the conclusion of a Senate trial.
He told Fox News: “I do think the president committed impeachable offences, but I don’t know what is going to land on the Senate floor, if anything.”
He said the president’s resignation is the “best path forward”, describing it as “the best way to get this person in the rear view mirror for us”.
Senator Lisa Murkowski of Alaska has also called for Mr Trump’s resignation.
But Mr Toomey admitted he was not optimistic it would happen before his term ends.
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Schwarzenegger likens Capitol rioters to Nazis
Politicians plan to formally introduce articles of impeachment on Monday in the House of Representatives – exactly one week before Democrat Joe Biden becomes the 46th president at noon on 20 January.
If passed by the House, the articles would be transmitted to the Senate for a trial, with senators acting as jurors who would ultimately vote on whether to acquit or convict Mr Trump.
If convicted by a two-third majority, requiring a number of Republicans to vote with the Democrats, then he would be removed from office and succeeded by the vice president.
The president has few fellow Republicans speaking out in his defence, with the former governor of California – and Hollywood legend – Arnold Schwarzenegger among those to have condemned him.
He has become increasingly isolated, holed up in the White House as he has been abandoned in the aftermath of the riot by many aides, leading Republicans, and two Cabinet members – both of whom are women.