WASHINGTON (AP) — Senate Republicans are poised to block the creation of a special commission to study the deadly Jan. 6 attack on the Capitol, dashing hopes for a bipartisan panel amid a GOP push to put the violent insurrection by Donald Trump’s supporters behind them.

Broad Republican opposition was expected in what would be the first successful Senate filibuster of the Biden presidency, even as the family of a Capitol Police officer who collapsed and died after the siege and other officers who battled rioters went office to office asking GOP senators to support the commission. The insurrection was the worst attack on the Capitol in 200 years and interrupted the certification of Democrat Joe Biden’s win over Trump.

A vote on the procedural motion was bumped to Friday after delays on an unrelated bill to boost scientific research and development pushed back the schedule.

Though the bill passed the House earlier this month with the support of almost three dozen Republicans, GOP senators said they believe the commission would eventually be used against them politically. And former President Trump, who still has a firm hold on the party, has called it a “Democrat trap.”

The expected vote is emblematic of the profound mistrust between the two parties since the siege, which has sowed deeper divisions on Capitol Hill even though lawmakers in the two parties fled together from the rioters that day. The events of Jan. 6 have become an increasingly fraught topic among Republicans as some in the party have downplayed the violence and defended the rioters who supported Trump and his false insistence that the election was stolen from him.

While initially saying he was open to the idea of the commission, which would be modeled after an investigation of the 9/11 terrorist attacks, Senate Republican leader Mitch McConnell turned firmly against it in recent days. He has said he believes the panel’s investigation would be partisan despite the even split among party members.

McConnell, who once said Trump was responsible for “provoking” the mob attack on the Capitol, said of Democrats, “They’d like to continue to litigate the former president, into the future.”

Still, a handful of Republicans — if not enough to save it — were expected to vote to move forward with the bill. Alaska Sen. Lisa Murkowski has said she will support the legislation because she needs to know more about what happened that day and why.