Republicans on Friday blocked the creation of an independent commission to investigate the Jan. 6 Capitol riot, using their filibuster power in the Senate for the first time this year to doom a full accounting for the deadliest attack on Congress in centuries.
With the vast majority of Republicans determined to shield their party from potential political damage that could come from scrutiny of the storming of the Capitol by a pro-Trump mob, only six G.O.P. senators joined Democrats to support advancing the measure. The final vote, 54 to 35, fell short of the 60 senators needed to move forward.
The vote was a stinging defeat for proponents of the commission, who had argued that it was the only way to assemble a truly comprehensive account of the riot for a polarized nation. Modeled after the inquiry into the Sept. 11, 2001 terrorist attacks, the proposed panel of experts would have been responsible for producing a report on the assault and recommendations to secure Congress by the end of the year.
The debate played out in the same chamber where a throng of supporters of former President Donald J. Trump, egged on by his lies of a stolen election and efforts by Republican lawmakers to invalidate President Biden’s victory, sought to disrupt Congress’s counting of electoral votes about five months ago.
Top Republicans had entertained supporting the measure as recently as last week. But they ultimately reversed course, and the House approved it with only 35 Republican votes. Leaders concluded that open-ended scrutiny of the attack would hand Democrats powerful political ammunition before the 2022 midterm elections — and enrage a former president they are intent on appeasing.
“I do not believe the additional extraneous commission that Democratic leaders want would uncover crucial new facts or promote healing,” said Senator Mitch McConnell of Kentucky, the minority leader. “Frankly, I do not believe it is even designed to do that.”
Though Mr. McConnell said he would continue to support criminal cases against the rioters and stand by his “unflinching” criticisms of Mr. Trump, the commission’s defeat is expected to embolden the former president at a time when he has once again ramped up circulation of his baseless and debunked claims.
In a matter of months, his lies have warped the views of many of his party’s supporters, who view Mr. Biden as illegitimate; inspired a rash of new voting restrictions in Republican-led states and a quixotic recount in Arizona denounced by both parties; and fueled efforts by Republican members of Congress to downplay and reframe the Capitol riot as a benign event akin to a “normal tourist visit.”
“People are just now beginning to understand!” Mr. Trump wrote in a statement on Thursday.
Democrats denounced the vote as a cowardly cover-up. They warned Republicans that preventing an independent inquiry — led by five commissioners appointed by Democrats and five by Republicans — would not shield them from confronting the implications of Mr. Trump’s attacks on the democratic process.
“What are you afraid of, the truth?” said Senator Chuck Schumer, Democrat of New York and the majority leader, addressing Republicans moments before the vote. “Are you afraid that Donald Trump’s big lie will be dispelled?”
“This is not a Democratic or Republican obligation,” he added. “This is an American obligation.”
The six Republicans who voted to advance debate on the commission included Senators Bill Cassidy of Louisiana, Susan M. Collins of Maine, Lisa Murkowski of Alaska, Rob Portman of Ohio, Mitt Romney of Utah and Ben Sasse of Nebraska. All but Mr. Portman had voted at an impeachment trial in February to find Mr. Trump guilty of inciting the insurrection.
A seventh Republican, Senator Patrick J. Toomey of Pennsylvania, missed the vote but said he would have voted to advance debate on the commission. He was one of 11 senators who missed the vote.