The lead prosecutor for US President Donald Trump's historic second impeachment has begun building his case for conviction at trial, asserting that Mr Trump's incitement of the mob that stormed the US Capitol was "the most dangerous crime" ever committed by a president against the United States.

A Senate trial could begin as soon as this week, just as Democrat Joe Biden is sworn in as the 46th president.

Congressman Jamie Raskin did not say when House Speaker Nancy Pelosi would send the single article of impeachment against Mr Trump - for "incitement of insurrection" - to the Senate, which will trigger the beginning of the trial. But Mr Raskin said "it should be coming up soon", as Ms Pelosi organises the formal transfer.

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The House voted to impeach Mr Trump last Wednesday, one week after the violent insurrection that interrupted the official count of electoral votes, ransacked the Capitol and left Congress deeply shaken.

Before the mob overpowered police and entered the building, Mr Trump told them to "fight like hell" against the certification of Mr Biden's election win.

"We're going to be able to tell the story of this attack on America and all of the events that led up to it," Mr Raskin said.

"This president set out to dismantle and overturn the election results from the 2020 presidential election. He was perfectly clear about that."

Democrats and the incoming administration are facing the challenge of reckoning with the Capitol attack at the same time as Mr Biden takes office and tries to move the country forward.

They say the Congress can do both, balancing a trial with confirmations of the new president's Cabinet and consideration of his legislative priorities.

Mr Raskin said Congress could not establish a precedent where "we just want to let bygones be bygones" just because Mr Trump has left office.

Yet it is clear that Democrats do not want the Senate trial to dominate Mr Biden's opening days.

Ms Pelosi said on Friday that Democrats intended to move quickly on Mr Biden's 1.9 trillion US dollars Covid aid and economic recovery package to speed up vaccinations and send Americans relief, calling it a "matter of complete urgency".

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Ron Klain, Mr Biden's incoming White House chief of staff, said he hoped Senate leaders, on a bipartisan basis, "find a way to move forward on all of their responsibilities. This impeachment trial is one of them, but getting people into the government and getting action on coronavirus is another one of those responsibilities".

It is unclear how many Senate Republicans, if any, would vote to convict Mr Trump.
Republican leader Mitch McConnell is telling his caucus that their decision on whether to convict the outgoing president will be a "vote of conscience".

His stance means the GOP leadership team will not work to hold senators in line one way or the other.

Mr McConnell is open to considering impeachment, but said he is undecided about how he would vote.

He continues to hold great sway in his party, even though convening the trial this week could be among his last acts as majority leader as Democrats prepare to take control of the Senate with the seating of two new Democratic senators from Georgia.

For Republican senators, the trial will be perhaps a final test of their loyalty to the defeated president and his legions of supporters in their states back home.

It will force a further re-evaluation of their relationship with Mr Trump, who lost not only the White House but majority control of the Senate, and a broader discussion about the future of the Republican Party as he leaves office.

No president has ever been convicted in the Senate, and it would take a two-thirds vote against Mr Trump, a high hurdle. But conviction is not outwith the realms of possibility, especially as corporations and wealthy political donors distance themselves from Mr Trump's brand of politics and the Republicans who stood by his attempts to overturn the election.

Mr Trump is the only president to be twice impeached, and the first to be prosecuted as he leaves the White House, an ever-more-extraordinary end to his tenure.