The impeachment trial of Donald Trump has passed a major test, with US senators voting that a post-presidential procedure is constitutional.

The US Senate voted 55-45 to block a Republican effort to upend plans for the former president’s impeachment trial on a charge that he incited the deadly January 6 assault on the US Capitol.

In an early test of the Senate’s impeachment drive, five Republicans joined Democrats on Wednesday (Australian time) to reject a motion by Republican Senator Rand Paul that would have required the chamber to vote on whether the trial violates the US Constitution.

Mr Paul and other Republicans contend that the proceedings are unconstitutional because Mr Trump left office last Wednesday (US time) and the trial will be overseen by Democratic Senator Patrick Leahy instead of US Chief Justice John Roberts.

“This proceeding, which would try a private citizen and not a president, vice-president or civil officer, violates the Constitution,” Mr Paul told his fellow senators after they had been sworn in as jurors for the trial set to begin on February 9.

“I want this body on record, every last person here: Is this how you think politics should be?” Mr Paul said.

“Are we going to put every politician in jail – are we going to impeach every politician who has used the words ‘fight’ figuratively in a speech? Shame!”

Democratic Senate Majority Leader Chuck Schumer dismissed Mr Paul’s argument as “flat-out wrong” and “a constitutional get-out-of-jail-free card” for presidents guilty of misconduct.

Most of the Senate’s 50 Republican lawmakers voted against a motion by Mr Schumer to kill Mr Paul’s proposal.

Mr Paul had predicted that support for his move would show the Senate incapable of convicting Mr Trump, which would require 67 votes. But some Republicans described Tuesday’s vote and the question of Mr Trump’s guilt as separate matters.

Tweet from @RandPaul

There is a debate among scholars over whether the Senate can hold a trial for Mr Trump now he has left office. Many experts have said “late impeachment” is constitutional, arguing presidents who engage in misconduct late in their terms should not be immune from the very process set out for holding them accountable.

Fellow Republican Senator Lisa Murkowski, who has been critical of Trump, rejected Mr Paul’s move.

“My review of it has led me to conclude that it is constitutional, in recognising that impeachment is not solely about removing a president, it is also a matter of political consequence,” Ms Murkowski said on Tuesday.

She joined fellow Republican senators Mitt Romney, Susan Collins, Ben Sasse and Patrick Toomey in opposing Mr Paul.

Mr Trump is the only president to have been impeached by the House of Representatives twice and the first to face a trial after leaving power. He also faces the possibility of being disqualified from future public office if convicted by two-thirds of the Senate.

The House approved a single article of impeachment on January 13, accusing him of inciting an insurrection with an incendiary speech to supporters before they stormed the Capitol on January 6. A police officer and four others died in the melee.

At least 17 Republicans would need to join all 50 Democrats for Mr Trump to be convicted, which appears unlikely.

Mr Trump remains a powerful force among Republicans and his supporters have vowed to mount election challenges to lawmakers in the party who support conviction.

-with agencies