Then outgoing US President Donald Trump addresses guests at Joint Base Andrews in Maryland on January 20, 2021. (ALEX EDELMAN / AFP)

Donald Trump's defenders in the Senate rallied around the former US president on Sunday ahead of his impeachment trial, dismissing it as a waste of time and arguing his speech before the US Capitol riot does not make him responsible for the violence of Jan 6.

"If being held accountable means being impeached by the House and being convicted by the Senate, the answer to that is no," said Republican Senator Roger Wicker of Mississippi, making clear his belief that Trump should and will be acquitted.

The Senate was set to launch the impeachment trial on Tuesday to consider the charge that Trump's fighting words to protesters at a Capitol rally as well as weeks of falsehoods about a stolen and rigged presidential election provoked a mob to storm the Capitol.

If being held accountable means being impeached by the House and being convicted by the Senate, the answer to that is no.

Roger Wicker, Republican Senator of Mississippi

Five people died as a result of the melee, including a police officer.

Other Republican senators including Rand Paul of Kentucky and Lindsey Graham of South Carolina also said on Sunday that they do not think Trump should be convicted.

It is unclear how long the trial will last, but what is clear is that as the trial opens, Democrats do not have the needed number of Republicans to join them to convict Trump.

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It would take a two-thirds majority of the 100-member Senate, or 67 votes, to convict him. That means 48 Democrats, two independents and 17 Republicans would need to vote in favor.

On a Jan 27 motion to declare the trial unconstitutional, only five Republicans voted with Senate Democrats to defeat it. After the vote, many Republicans indicated Trump's acquittal was a foregone conclusion.

Republican Senator Pat Toomey of Pennsylvania was one of those five Republicans. He said on Sunday it's "very unlikely" the Senate will vote to convict Trump, noting the Jan 27 motion.

Opinion poll

A survey from The Associated Press-NORC Center for Public Affairs Research says nearly two-thirds of US citizens believe Trump bears at least a moderate amount of responsibility for the breach of the Capitol, including half who say he bears a great deal or quite a bit. Just over a third say he bears little to no responsibility.

Fewer US citizens, 47 percent, believe the Senate should vote to convict Trump after his impeachment trial. Another 40 percent say he should not be convicted, and 12 percent are not sure.

Trump's first impeachment trial in 2020, in which he was acquitted on charges that he abused power by pressuring Ukraine to investigate now-President Joe Biden, lasted almost three weeks.

Last week, the House's lead impeachment manager, Maryland Representative Jamie Raskin sent a letter to Trump's legal team asking that he testify under oath and submit to cross-examination either before or during the trial.

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Trump lawyer Bruce Castor quickly responded, saying Trump wouldn't testify and called the request a "publicity stunt in order to make up for the weakness of the House managers' case".