Colorado’s three House Republican members were not among the 35 GOP lawmakers who voted Wednesday to create an independent, bipartisan commission to investigate the Jan. 6 attack on the U.S. Capitol.

The measure won approval 252-175 in the Democratic-controlled House over objections from Republican leaders and former President Donald Trump, with all four of the state’s Democrats voting in favor.

The legislation, modeled on the creation of an investigation into the Sept. 11, 2001, attacks, would establish a 10-member commission, with five members appointed by congressional leaders from each major party. It would be tasked with making recommendations for securing the Capitol and preventing another insurrection by the end of the year.

Colorado Democrats said the investigation was needed to determine how a violent mob of Trump supporters stormed the Capitol in an attempt to overturn certification of President Joe Biden’s election.

“Jan. 6 was one of the darkest days in our nation’s history, and the American people deserve to know exactly what happened,” said U.S. Rep. Diana DeGette, D-Denver, who was one of nine House impeachment managers who prosecuted a case against Trump for inciting the riot.

She said impeaching Trump for a second time — after he left office — was meant to “shed a light on what happened in hopes of preventing such violence from ever happening again in this country,” and that the commission would have the same goal. “We want to know what happened, why it happened, and what needs to be done to ensure it never happens again.”

Saying it shouldn’t be a partisan issue, DeGette added that “the American people should be outraged at anyone who voted today to cover up the truth.”

U.S. Rep. Ken Buck, R-Windsor, said in a statement that the attack on the Capitol was wrong and that he “unequivocally condemned the violence and urged that the perpetrators be prosecuted to the fullest extent of the law” but said he was voting against legislation he called “a blatant exercise in partisanship” that was “too narrow in scope.”

“I would support a truly bipartisan commission to investigate the Jan. 6 attack and other recent political violence, including the death of the Capitol Police officer at a Capitol barricade last month,” Buck said. “I am disappointed that House Democrats seem to have prioritized their political agenda over finding facts.”

Buck noted House Speaker Nancy Pelosi originally proposed seating more Democrats on the commission than Republicans, though the Republican who negotiated the resolution on the Homeland Security Committee, New York Rep. John Katko — like Buck, a former prosecutor — argued contrary to Buck’s assertion on the House floor.

“I encourage all members, Republicans and Democrats alike, to put down their swords for once, just for once, and support this bill,” Katko said. “This is about fact. It is not partisan politics.”

U.S. Rep. Jason Crow, D-Aurora, one of the impeachment managers in Trump’s first Senate trial, began his written statement nearly identically to DeGette’s.

“Jan. 6th was one of the darkest days of our democracy,” Crow said after the vote. “Only a few months later, people in the public trust — many who were present during the attack — are already trying to cover up what happened.” He added: “The only way to move forward is with truth and accountability.”

U.S. Rep. Joe Neguse, D-Lafayette, who served alongside DeGette as an impeachment manager earlier this year, said in a TV interview that he viewed the vote as “a real binary choice as to whether or not folks will choose to side with the truth and support a bipartisan effort to appoint a commission … or you can side with the president, with President Trump.”

The other Colorado Republicans who voted against the resolution — U.S. Reps. Doug Lamborn of Colorado Springs and Lauren Boebert of Silt — didn’t respond to requests for comment.

The Associated Press contributed to this report.