Senate Republicans on Friday blocked the creation of a bipartisan panel that would have investigated the January 6 attack on the Capitol, refusing to back down amid emotional appeals from those who experienced the riot first-hand.
The Senate vote was 54-35, short of the 60 votes needed to pass a bill that would have formed a 10-member commission evenly split between the two parties.
The vote was another sign of Republican fealty to former president Donald Trump and an overtly political effort to shift the focus off of the violent insurrection of his supporters.
Though the January 6 commission bill passed the House earlier this month with the support of almost three dozen Republicans, senators from the party said they believe the commission would eventually be used against them politically.
Mr Trump, who still has a firm hold on the party, has called it a “Democrat trap".
The vote is emblematic of the profound mistrust between the two parties since the siege, especially among Republicans, as some in the party have downplayed the violence and defended the rioters who supported Mr Trump and his false insistence that the election had been stolen from him.
“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 Dick Durbin, a Democratic senator from Illinois. “That tells you what’s wrong with the Senate and what’s wrong with the filibuster.”
The Republicans' use of a filibuster was the first successful use of the measure this year to halt Senate legislative action, reviving pressure on Democrats to do away with the procedural tactic that critics say has lost its purpose.
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 have needed the support of 10 Republicans to move to the commission bill.
The House had approved the measure with some Republican support, but the Senate filibuster has sparked fresh debate over whether the time has come for Democrats to change the rules and lower the threshold to 51 votes to take up legislation.
Mr Trump has made it clear he opposes the formation of any panel to investigate the events of January 6.
Democrats have said 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.
Before the vote, the mother of late Capitol Police officer Brian Sicknick said on Wednesday that she would meet senators to try to persuade them to act.
Sicknick was among many officers protecting the building. He collapsed after engaging with the rioters and died the next day.
“I suggest that all congressmen and senators who are against this bill visit my son’s grave in Arlington National Cemetery and, while there, think about what their hurtful decisions will do to those officers who will be there for them going forward,” Gladys Sicknick said.
“Putting politics aside, wouldn’t they want to know the truth of what happened on January 6?” she said.
Thirty-five Republicans, including Utah senator Mitt Romney and Alaska senator Lisa Murkowski, backed the bill, but most followed Senate minority leader Mitch McConnell, who has declared the bill a “purely political exercise”, as Senate committees are already looking into security shortfalls.
Republicans also say a bipartisan Senate report, expected to be released next month, will be sufficient to fix security problems in the Capitol.
Mr McConnell, who once said Mr Trump was responsible for “provoking” the mob 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 Mr 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 refuted by courts and election officials across the country.
The commission vote will become “exhibit A” on why the filibuster needs to be changed, said Grant Tudor, a policy advocate at the Protect Democracy organisation.
"They are shining a spotlight: There is no bill that stands up to Trump and the 'Big Lie' that can get 10 Republicans," said Eli Zupnick of Fix Our Senate, which advocates for filibuster changes.
Four of the rioters died during the insurrection, including a woman who was shot and killed by police as she tried to break into the House chamber with members of Congress still inside and a police officer who collapsed and died afterward of what authorities said were natural causes.
Two police officers took their own lives in the days after the riots.
Dozens of the officers defending the Capitol were brutally beaten by the rioters. Hundreds of people have been arrested.