The vote on Thursday would be the first successful use of a filibuster in the Biden presidency to halt Senate legislative action. Most Republicans oppose the bill that would establish a commission to investigate the attack by Donald Trump supporters over the election.

"We have a mob overtake the Capitol, and we can't get the Republicans to join us in making historic record of that event? That is sad," said Senator Dick Durbin of Illinois, the No. 2 Senate Democrat.

"That tells you what's wrong with the Senate and what's wrong with the filibuster."

The filibuster is a time-honoured Senate tradition that requires a vote by 60 of the 100 senators to cut off debate and advance a bill. With the Senate evenly split 50-50, Democrats would need support of 10 Republicans to move to the commission bill, sparking fresh debate over whether the time has come to change the rules and lower the threshold to 51 votes to take up legislation.

The House already approved the measure with 35 Republican votes. But Trump has made it clear he opposes the formation of any panel to investigate the January 6 siege, when a violent mob of his supporters broke into the Capitol in a failed effort to overturn Joe Biden's election.

Democrats are warning that if Republicans are willing to use the filibuster to stop an arguably popular measure, it shows the limits of trying to broker compromises, particularly on bills related to election reforms or other aspects of the Democrats' agenda.

"There is no excuse for any Republican to vote against this commission," said Democrat Senator Joe Manchinwhile still making clear that he would not support efforts to do away with the filibuster.

"I'm not ready to destroy our government," Manchin said.

"I think we'll come together. You have to have faith there's 10 good people."

Mostly, the GOP senators will follow Senate Republican leader Mitch McConnell, who has declared the bill a "purely political exercise," since Senate committees are already looking into security shortfalls.

McConnell, who once said Trump was responsible for "provoking" the attack on the Capitol, now says of Democrats: "They'd like to continue to litigate the former president, into the future."

The talks over potential changes to the legislation come as Republicans have struggled over how to respond to the insurrection as many in their party have remained loyal to Trump.

The former president told his supporters the morning of January 6 to "fight like hell" to overturn his defeat. He has repeatedly said the election was stolen, even though his claims have been rejected by courts and election officials across the country.

Four protesters died during the insurrection, including a woman who was shot and killed by police as she tried to break into the House chamber with lawmakers still inside.

Dozens of the officers defending the Capitol were injured. Hundreds of people have been arrested.

Australian Associated Press