Call it a coup, an insurrection, a riot, a siege: Whatever else Wednesday’s brief takeover of the U.S. Capitol by pro-Trump extremists looked like, it was also a profound failure of policing. Despite the presence of both Vice President Pence and House Speaker Nancy Pelosi — second and third in the presidential line of succession — and despite the hundreds of members of Congress gathered in joint session, angry Trump supporters were able to breach perimeter after perimeter, at times simply walking past Capitol Police officers who made no apparent effort to stop them. Members of the mob scaled walls, smashed doors and windows, vandalized works of art, and stole laptops, correspondence and personal items from offices, forcing the emergency evacuation of lawmakers and staff. It was the largest assault on the Capitol since the British attack during the War of 1812.

By day’s end, four people were dead, and many more, including more than 50 police officers, were injured. One officer injured Wednesday died Thursday. Yet only a handful of the rioters were arrested: Most simply strolled out of the Capitol — some proudly displaying stolen items — as easily as they had strolled in.

 The failure of the Capitol Police to anticipate, prevent and respond to the violence is baffling and appalling. But in many ways, it’s a direct consequence of the way the police agency that protects the legislative branch is organized, with far too little accountability or diversity, jumbled oversight, and too many opportunities for politics to creep into its mission.

There was every reason to expect that the pro-Trump rallies planned for Wednesday would turn ugly and violent, probably with threats to Congress. In September, the FBI and the Department of Homeland Security warned that white-supremacist groups — not foreign organizations or left-wing extremists — presented the gravest terrorist threat within the United States. Acting deputy homeland security secretary Ken Cuccinelli testified at a Sept. 24 Senate hearing about the high “lethality” of white-supremacist groups, noting, “It isn’t a belief, it’s just looking at the data.” The next week, an FBI intelligence report noted the increased threat of violent extremism posed by right-wing groups aligned with the “boogaloo” movement.

And there were numerous, specific warning signs about Wednesday’s pro-Trump gatherings, which were timed to protest the joint session of Congress at which President-elect Joe Biden would be formally certified as the winner of the electoral college vote. Previous marches by many of the same organizations and individuals involved in Wednesday’s protests had erupted into chaos. Earlier in the week, D.C. police arrested the leader of the Proud Boys for his role in vandalizing the property of historic Black churches during a Dec. 12 protest that also saw four people stabbed and more than 30 others arrested. In the days leading up to Wednesday, scores of media reports highlighted the growing threat of violence from far-right actors.

In his own remarks around noon on Wednesday, President Trump called on his supporters to go to the Capitol to protest what he falsely claimed was an “egregious assault on our democracy” — the certification of a legitimate election result — advising them, “You will never take back our country with weakness.” By 1:10 p.m., just minutes after the joint session began, the pro-Trump crowd was shoving past police and onto the grounds of the Capitol.

Yet the Capitol Police, which has exclusive jurisdiction over the Capitol and its grounds, appears to have been caught entirely flat-footed. Video footage shows only a handful of officers — in ordinary uniforms, not riot gear — at the outer perimeters of the Capitol, the first line of defense against trespassers. (On Thursday, after most of the rioters were long gone, a by-then-unnecessary security fence started going up around the Capitol.) When crowds pressed toward them, many officers simply retreated, not making any apparent effort to physically block protesters from pushing past the gates.