"The evidence is Trump's own words, recorded on video," Blumenthal said. "It's a question of whether Republicans want to step up and face history."

Although current Senate majority leader Mitch McConnell has privately told advisers that he approves of the impeachment drive and believes it could help his party purge itself of Trump, he refused to begin the proceedings this week while he is still in charge.

House Speaker Nancy Pelosi of California has discretion over when to transmit the article of impeachment, formally initiating the Senate proceeding. Some Democrats said she might wait until January 25 or longer to allow more time for the Senate to put in place Biden's national security team to respond to threats of violence from pro-Trump extremists.

With Republicans fractured after the president's bid to overturn the election inspired a rampage, many of them were trying to gauge the dynamics of a vote to convict Trump. Doing so would open the door to disqualifying him from holding office in the future.

A cautionary tale was playing out in the House, where a faction of Trump's most ardent allies was working to topple Liz Cheney of Wyoming, the number three Republican, from her leadership post. Cheney had joined nine other members of the party who voted with Democrats to charge the president with "incitement of insurrection".

Most Senate Republicans stayed silent about their positions. But Alaskan Senator Lisa Murkowski, one of the president's leading critics, signaled on Thursday (Friday AEDT) that she was among a small group in her party so far considering convicting Trump.

Though she did not commit to finding the president guilty, saying she would listen carefully to the arguments on both sides, she strongly suggested that she was inclined to do so.

"On the day of the riots, President Trump's words incited violence, which led to the injury and deaths of Americans — including a Capitol Police officer — the desecration of the Capitol, and briefly interfered with the government's ability to ensure a peaceful transfer of power," Murkowski said.

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Murkowski joined a small group of other Republican Senators — including Ben Sasse of Nebraska, Mitt Romney of Utah, Patrick Toomey of Pennsylvania and Susan Collins of Maine — who have said they hold the president responsible for the siege and will weigh the impeachment charge. Romney was the only Republican last year to vote to convict Trump when the House impeached him for pressuring Ukraine to incriminate Biden.

But it remained unclear whether there would be 17 Republican senators who would agree to convict Trump, the minimum number required to make up a two thirds majority. South Carolina Senator Lindsey Graham worked feverishly to whip up opposition to a conviction, arguing that it would only inflame a dangerously divided nation.

With McConnell sending mixed signals about where he would come down, Republican strategists and senior aides on Capitol Hill believed he could ultimately swing the result one way or another.

If the Senate did convict, it could proceed to disqualify Trump from holding office again with only a simple majority vote, a prospect motivating some on both sides.

Senators considering breaking with the president needed to look no further than Cheney to understand the risks.

In a petition being privately circulated among Republicans on Capitol Hill, a group of lawmakers led by Andy Biggs of Arizona, chair of the ultraconservative Freedom Caucus, and Matt Rosendale of Montana, claimed that Cheney's vote to impeach the president had "brought the conference into disrepute and produced discord".

Calling hers a "vote of conscience," Cheney brushed aside calls to step down, saying, "I'm not going anywhere."

In the Senate, leaders were facing a daunting set of questions about the trial with little history to guide them. The House has never impeached a president so close to the end of his term, and no former president has ever been tried in the Senate.

Some Republicans, led by Senator Tom Cotton of Arkansas, pointed to those precedents to argue that the chamber did not have jurisdiction to try Trump, but many legal scholars appeared to disagree.

Democrats faced the vexing task of trying to manage a trial just as Biden will take office. Once the House formally sends its article to the Senate, a trial must commence almost immediately, and rules dictate that all other business come to a near immediate halt and remain frozen until a verdict is reached.

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Democrat leader in the Senate Chuck Schumer worked to agree with McConnell on trial rules that could get around those strictures. The goal was to divide the Senate's days so the chamber could work on confirming members of Biden's Cabinet and considering his stimulus package in the morning and then take up the impeachment trial in the afternoon.

"Everything we are talking about is being invented out of whole cloth," saidDemocrat Senator Christopher Murphy. "We have never tried a president after they left office. We've never had an insurrection against the Capitol. We've never held a trial while we are confirming a Cabinet. All of this is first impression."

The New York Times