▶ Watch Video: Inspector general’s report slams U.S. Capitol Police failures ahead of January 6 riot Washington — Precisely three months after the January 6 assault on the Capitol, dozens of former senior national security, military and elected officials from both sides of the aisle urged lawmakers in Congress to establish an independent bipartisan commission to investigate the attack. “We write to encourage this Congress to establish an independent and bipartisan national commission to investigate the January 6th assault of the U.S. Capitol Complex and its direct causes, and to make recommendations to prevent future assaults and strengthen the resilience of our democratic institutions,” the letter signed by 140 officials read. The long list of officials includes nearly two dozen ambassadors, six former senators, four former secretaries of homeland security and two members of the 9/11 Commission. The letter warned of “an exigent and growing threat” to the American public following the riot that left five people dead, including a Capitol Police officer. “The events of January 6th exposed severe vulnerabilities in the nation’s preparedness for preventing and responding to domestic terrorist attacks,” the message said. Last month, U.S. intelligence agencies issued a joint assessment of the national security threat posed by domestic violent extremism. An unclassified summary of the report by the Office of the Director of National Intelligence said domestic terrorism poses an “elevated threat” to the homeland in 2021 and predicted that social and political factors, including the coronavirus pandemic and “emboldening impact of the violent breach of the U.S. Capitol,” will “almost certainly” spur domestic violent extremists to engage in further violence. But congressional efforts to secure bipartisan cooperation to create an independent commission dedicated to investigating the response to the attack have stalled, even as the Justice Department has since charged more than 350 people with breaching the Capitol. Those arrested include at least 57 alleged members of extremist groups, including the Proud Boys, Oath Keepers, Three Percenters, Texas Freedom Force and adherents of the conspiracy theory QAnon. Legislative efforts to create an independent, bipartisan panel hit a snag in February over disagreements between Democrats and Republicans over the scope and structure of the review, which would likely examine former President Donald Trump’s role in the deadly assault. Objecting to Speaker Nancy Pelosi’s original proposal, GOP lawmakers voiced their opposition to granting President Biden three appointments to the commission, in addition to one each from House and Senate leaders from both parties. Under the speaker’s proposed plan, Democrats would hold an overall 7-4 majority on the commission. The 9/11 Commission, which serves as the model for independent investigatory panels, consisted of an equal number of Republicans and Democrats. Pelosi has since expressed an openness to negotiating the terms of the commission. “Let me just say I am committed to finding the truth,” Pelosi said in a virtual press briefing two weeks ago. “Now, you’re making a fuss about the numbers and this, that. That’s all negotiable. That’s incidental.” Unable to find common ground on an independent commission, seven House Committees launched an investigation into the federal government’s handling of the attack in late March. The panels dispatched letters to 16 agencies across the federal government requesting all communications relating to the January 6 session of Congress, when lawmakers met to finalize the results of the 2020 presidential election. The broad review by committees demanded relevant documents and messages dated between December 1, 2020 and January 20, 2021. The former officials who signed Tuesday’s letter said that a commission in the style of the 9/11 Commission would complement congressional and law enforcement investigations into the attack and the government’s response. “In the wake of September 11th, the administration and Congress jointly acknowledged that the attack’s causes were complex and that an independent and well-equipped national commission was an essential tool to aid the federal government,” the letter read. “Congressional inquiries, law enforcement activities, and a national commission not only worked in parallel, but critically complemented each other’s necessary work. An independent commission should not supplant the ongoing work by the legislative and executive branches, but it can uniquely support them by providing comprehensive and expert recommendations for Congress to act upon.” The group warned that failure to establish such a commission would “leave the Capitol, and the nation, vulnerable to future attacks.” Rebecca Kaplan contributed to this report.