The US Senate began hearing final arguments on Saturday local time in the impeachment trial of Donald Trump as the top Republican senator said he would vote to acquit the former president of inciting the deadly 6 January assault on the Capitol.
Republican Senate Minority Leader Mitch McConnell's decision means Mr Trump is all but certain to be acquitted by the Senate of the charge of inciting an insurrection by his supporters.
Before moving to final arguments, the proceedings were interrupted for a few hours after House prosecutors, in a surprise move, said they wanted to call witnesses at the trial.
House impeachment manager Jamie Raskin said he wanted to call a Republican lawmaker as a witness but eventually agreed with Mr Trump's defense lawyers just to have her testimony entered into evidence.
House impeachment manager Joe Neguse speaks at the second impeachment trial of Donald Trump in the Senate in Washington on Wednesday. Source: Senate Television
Mr Trump's lawyers had threatened in response to call witnesses of their own, including Vice President Kamala Harris, Nancy Pelosi, the Democratic speaker of the House of Representatives, and others.
The Senate voted 55-45 to allow witnesses but senators, House prosecutors and defense lawyers then hammered out an agreement allowing the trial to proceed to closing arguments.
The four hours of final arguments will be split equally between both sides with the House prosecutors going first.
A vote on whether to acquit or convict the 74-year-old former Republican president is expected later on Saturday afternoon.
Mr Raskin had wanted Representative Jamie Herrera Beutler to testify after she released a statement about the events of 6 January.
Herrera Beutler, a Republican from Washington state, was one of 10 Republican lawmakers who voted to impeach Mr Trump in the House of Representatives.
In her statement, she said Republican House Minority Leader Kevin McCarthy had called Mr Trump while the attack was ongoing and implored him to call off the rioters.
"When McCarthy finally reached the president on January 6 and asked him to publicly and forcefully call off the riot, the president initially repeated the falsehood that it was Antifa that had breached the Capitol," Ms Beutler said.
"McCarthy refuted that and told the president that these were Trump supporters," the congresswoman said.
"That's when, according to McCarthy, the president said: 'Well, Kevin, I guess these people are more upset about the election than you are,'" she said.
'A close call'
Mr Trump was impeached by the Democratic-controlled House on 13 January for inciting the attack on the US Capitol by his supporters, who were seeking to block congressional certification of Democrat Joe Biden's 3 November election victory.
A conviction in the 100-member Senate - which is evenly split between Democrats and Republicans - would require a two-thirds majority and appears highly unlikely after Mr McConnell said he would vote to acquit.
"While a close call, I am persuaded that impeachments are a tool primarily of removal and therefore we lack jurisdiction," Mr McConnell said in an email to his Republican colleagues.
"The Constitution makes perfectly clear that Presidential criminal misconduct while in office can be prosecuted after the President has left office," he said. "Given these conclusions, I will vote to acquit."
Mr Trump's defense lawyers argued on Friday that the former president bears no responsibility for the attack on Congress and wrapped up their presentation in just three hours.
Senate Majority Leader Mitch McConnell Source: AAP
This followed two days of evidence from Democratic impeachment managers centered around harrowing video footage of the mob assault on the Capitol.
Mr Trump's defense lawyers called the impeachment unconstitutional and an "act of political vengeance."
They argued that Mr Trump's rally speech near the White House that preceded the 6 January attack, when he told supporters to "fight," was merely rhetorical.
Seeking to turn the table on the Democrats' powerful use of video evidence, defense lawyers played their own compilations showing Democratic lawmakers at different times using the word "fight."
House impeachment managers charge that after losing to Mr Biden, Mr Trump deliberately stoked tension with a campaign of lies claiming there had been mass voter fraud.
On 6 January he staged a fiery rally near the White House, calling on the crowd to march on Congress, which was in the process of certifying Mr Biden's victory.
The mob then stormed the Capitol, disrupting the certification. Five people, including a police officer and a woman shot during the unrest, died in the mayhem.
