Senate Republicans are expected to block a bill creating a commission to investigate the pro-Trump riot at the US Capitol on January 6, preventing a high-profile probe into the attack that led to the deaths of five people and about 140 police officers injured.

The timing of the vote is uncertain. Senators had expected to take a procedural vote as soon as Thursday night before heading out on weeklong Memorial Day recess. But a stalled debate on an unrelated bill aimed at increasing US competitiveness with China pushed back the timing for the commission vote. Senators were on the floor of the Senate late Thursday night to try to solve the impasse.

Despite the delay, the commission vote is still expected to fall short of the 60 votes it needs to advance. The refusal of at least 10 Republican senators to vote for the commission underscores the deeply partisan divide that has emerged over the insurrection earlier this year and comes at a crucial time for Capitol Hill where Democrats are struggling to advance President Joe Biden's agenda. Some Democrats are citing the resistance by Republicans as a sign for why the Senate should blow up the 60-vote threshold to pass most legislation, given the narrowly divided chamber.

While some Republicans said months ago that a 9/11-type commission into the security of the Capitol was a necessity, they've since argued that it wouldn't yield any new information amid other law enforcement investigations and arrests. Their opposition has infuriated Democrats, who assert that Republicans are trying to protect themselves ahead of the midterm elections.

"There is no excuse for any Republican to vote against this commission since Democrats have agreed to everything they asked for," West Virginia Democratic Sen. Joe Manchin told CNN on Thursday. "(Senate Minority Leader Mitch) McConnell has made this his political position, thinking it will help his 2022 elections. They do not believe the truth will set you free, so they continue to live in fear."

The House-passed legislation aims to create a 10-person panel to figure out what happened, including the law enforcement's "preparedness and response," and then report recommendations in order "to prevent future acts of targeted violence and domestic terrorism."

The backstory

While the mob failed to stop Congress' certification of Biden's 2020 victory, 147 Republicans voted to object to it. Now most Republicans in Congress oppose a new commission delving into the attack on the Capitol, charging that Democrats want to use it as a political tool in the 2022 midterm elections. Democrats have criticized Republicans in turn for siding with former President Donald Trump, who continues to falsely claim that the 2020 election was "stolen" from him, in the national security matter.

White House press secretary Jen Psaki reiterated on Thursday that Biden supports setting up the new commission.

"He wants to make sure that's law because that was a dark day in our history," said Psaki. "He thinks we should not only take a moment to recognize that but also prevent it from happening ever in the future."

What McConnell and Schumer are saying

McConnell objects to building the commission, citing ongoing law enforcement investigations and the hundreds of arrests made, as well as lower-profile activities in congressional committees. Earlier this week, McConnell said that the bill "is a purely political exercise that adds nothing to the sum total of information."

"I do not believe the additional, extraneous 'commission' that Democratic leaders want would uncover crucial new facts or promote healing," McConnell said. "Frankly, I do not believe it is even designed to."

Senate Majority Leader Chuck Schumer argued that Republicans oppose the bill not because of how the commission is structured but because of politics.

"The truth of the matter seems to be that Senate Republicans oppose the commission because they fear that it might upset Donald Trump and their party's midterm messaging," said Schumer.

How the commission would work

The commission would attempt to find bipartisan consensus. The Democratic and Republican leaders of the House and Senate evenly split the selection of its 10 members. A subpoena can only be issued to compel witness testimony if it has the support of the majority of members, or if the commission's chairperson, chosen by Democrats, and the vice-chairperson, chosen by Republicans, come to an agreement.

The commission is also required to submit to the President and Congress a final report by the end of 2021 and dissolve 60 days thereafter -- about nine months before the 2022 elections.

The search for 10 GOP votes

Last week, the House passed the bill 252-175, with 35 Republicans joining Democrats.

Two Democratic senators, Manchin and Kyrsten Sinema of Arizona, have publicly urged Senate Republican senators to also back the bill. But only three -- Sens. Mitt Romney of Utah, Susan Collins of Maine and Lisa Murkowski of Alaska -- have expressed their support for advancing the legislation, and Democrats need 10. The vast majority of the 50 Senate Republicans are expected to oppose it; West Virginia Sen. Shelley Moore Capito told CNN that the issue has become "too politicized."

Collins has pushed for a commission, saying Thursday, "We owe it to the brave men and women who defended our lives that day."

But she wants the Senate to vote on an amendment addressing her two main concerns with the bill: the chairperson appoints the staff (in consultation with the vice-chairperson), and the commission's work could last into the first two months of an election year. Schumer has said a separate Republican staff "warring" with a Democratic staff would be untenable.

Republicans' opposition to the bill has again led some Democrats to call for eliminating the Senate's 60-vote threshold to advance most legislation. All 50 Democratic senators would have to agree to do that, which would fundamentally change how federal legislation is passed, but Sinema, Manchin and other Democrats have opposed nuking the filibuster.

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

Romney's warning for Republicans

When asked Wednesday how blocking the bill would reflect upon his party, Romney said: "Not well."

"Republicans would be seen as not wanting to let the truth come out," said Romney. "I don't believe that's what's the motivation but I think that's the perception."

"I think the real motivation is that Republicans feel that the January 6 commission is designed by Democrats to further their political interests and to help them for the '22 elections," he added. "Republicans don't feel that's a cause they want to join in."

By Alex Rogers, Manu Raju and Ted Barrett, CNN