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

Asked if Congress could consider other punishment, such as censure, Wicker said the Democratic-led House had that option earlier but rejected it in favour of impeaching him.

“That ship has sailed,” he said.

The Senate is 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. Five people as a result of the melee, including a police officer.

Many senators including Senate Republican leader Mitch McConnell immediately denounced the violence and pointed a finger of blame at Trump.

Following the riot, Wicker said Americans “will not stand for this kind of attack on the rule of law” and without naming names, said “we must prosecute” those who undermine democracy.

But with Trump now gone from the presidency, Republicans have shown little political appetite to take further action, such as an impeachment conviction that could lead to barring him from running for future office.

Those partisan divisions appear to be hardening ahead of Trump's trial, a sign of his continuing grip on the GOP.

On Sunday, Wicker described Trump's impeachment trial as a “meaningless messaging partisan exercise."

When asked if Trump's conduct should be more deserving of impeachment than President Bill Clinton's, whom Wicker voted to impeach, he said: “I'm not conceding that the President Trump incited an insurrection.”

Clinton's impeachment, in 1998, was sparked by his false denial in a deposition of a sexual relationship with a White House intern.

Republican Sen. Rand Paul of Kentucky dismissed Trump's trial as a farce with “zero chance of conviction,” describing Trump's words to protesters to “fight like hell” as Congress was voting to ratify Joe Biden's presidential victory as “figurative” speech.

“If we're going to criminalise speech, and somehow impeach everybody who says, Go fight to hear your voices heard,' I mean really we ought to impeach Chuck Schumer then,” Paul said, referring to the now Democratic Senate majority leader and his criticisms of Justices Neil Gorsuch and Brett Kavanaugh.

“He went to the Supreme Court, stood in front of the Supreme Court and said specifically, Hey Gorsuch, Hey Kavanaugh, you've unleashed a whirlwind. And you're going to pay the price.'”

Paul noted that Chief Justice John Roberts had declined to preside over this week's impeachment proceeding because Trump was no longer president.

Democratic Sen. Patrick Leahy will preside over the trial as Senate president pro tempore.

“It is a farce, it is unconstitutional. But more than anything it's unwise, and going to divide the country,” Paul said.

Last month, Paul forced a vote to set aside the trial as unconstitutional because Trump is no longer in office, which legal experts say is disputable. But the vote suggested the near impossibility in reaching a conviction in a Senate where Democrats hold 50 seats but a two-thirds vote — or 67 senators — would be needed to convict Trump.

Forty-four Republican senators sided with Paul and voted to oppose holding an impeachment trial at all.

Five Republican senators joined with Democrats to reject Paul's motion: Mitt Romney of Utah, Ben Sasse of Nebraska, Susan Collins of Maine, Lisa Murkowski of Alaska and Pat Toomey of Pennsylvania.

Some Republicans have said the vote doesn't “bind” them into voting a particular way on conviction, with Republican Sen. Bill Cassidy on Louisiana saying Sunday he would listen carefully to the evidence. But even Trump's sharper GOP critics on Sunday acknowledged the widely expected outcome.

“You did have 45 Republican senators vote to suggest that they didn't think it was appropriate to conduct a trial, so you can infer how likely it is that those folks will vote to convict,” said Toomey, who has made clear he believes Trump committed “impeachable offenses.”

“I still think the best outcome would have been for the president to resign” before he left office, he said. “Obviously he chose not to do that.”

Republican Sen. Lindsey Graham of South Carolina, one of Trump's ardent defenders, said he believes Trump's actions were wrong and “he's going to have a place in history for all of this,” but insisted it's not the Senate's job to judge.

“It's not a question of how the trial ends, it's a question of when it ends,” Graham said.

“Republicans are going to view this as an unconstitutional exercise, and the only question is, will they call witnesses, how long does the trial take? But the outcome is really not in doubt.”