The storming of the U.S. Capitol offers a reminder that the most devastating attacks often aren’t the ones that take us by surprise but those we see coming and don’t take adequate steps to avoid.

Officials who planned for Wednesday’s pro-Trump rallies knew the “protesters” (that mild term seems laughable now) would march on the Capitol. They knew some of the extremists might try to break through the perimeter. But they decided to trust the assurances of the Capitol Police that they could control the situation.

The reassuring words I heard from senior officials are haunting: “I can see no situation where the cops can’t handle it,” one told me, after describing the possibility of an assault on the Capitol. That’s agonizing to replay. This disaster didn’t sneak up on the Defense and Justice departments and the mayor’s office; they saw it approaching. But they thought the 6,000 to 8,000 law enforcement officers available were adequate to handle the problem.

Now that looks like a wrong call. Law enforcement did indeed get the situation under control by Wednesday night, with limited bloodshed. But that was only after the Capitol had been invaded and ransacked, members of Congress terrorized, four people died, and the most precious symbol of American democracy desecrated.

Some mistakes are obvious: The FBI underestimated the number of protesters, predicting a maximum of 20,000, which turned out to be less than half the number who showed up. The Capitol Police didn’t stand their ground at the perimeter or at the Capitol itself. The mayor was slow to request additional troops from the D.C. National Guard. The acting attorney general was similarly tardy in ordering elite FBI units into the Capitol. And the Pentagon brass worried more about avoiding politicization of the military than about stopping an insurrection.

In a seeming acknowledgment of the inadequate response, Capitol Police Chief Steven A. Sund announced Thursday night that he was resigning. The Associated Press reported that the Capitol Police had turned down offers of additional support from the National Guard and the FBI before the disastrous invasion of the Capitol on Wednesday afternoon.

But as we look for who to blame in this catastrophe, let’s focus on the real culprits: President Trump, who incited the rioters and urged them toward the Capitol; the 13 Republican senators and 138 House members who challenged President-elect Joe Biden’s victory and egged on the insurgents; and the smug, self-appointed patriots who trashed the people’s house. Trump should face legal action for fomenting this riot. The members who risked the lives of their colleagues by encouraging the fanatics should be censured. The insurgents who ransacked the Capitol should be arrested and prosecuted.

D.C. Mayor Muriel E. Bowser (D) and Gen. Mark A. Milley, the chairman of the Joint Chiefs of Staff, both tried to avert a militarization of the response to protests, similar to what happened in D.C. and many other cities during the racial-justice protests that followed George Floyd’s death. Wanting to avoid overreaction, they probably underreacted. That carried costs, but also benefits.

A “net assessment” of the Capitol siege (to use the term beloved by Pentagon strategists) is that Trump’s ragtag army of sedition has lost big. Their narrative of victimization has turned upside down; their claims of election fraud have been demonstrated to be false. Biden’s election has been certified, and leading Republicans such as Vice President Pence and Senate Majority Leader Mitch McConnell (Ky.) have finally broken from Trump.

More force is coming to avoid any repeat in the run-up to Biden’s inauguration: The Pentagon, working with the mayor’s office, is mobilizing more than 6,000 additional National Guard troops, calling on nearby states such as Maryland, Pennsylvania, New Jersey, Delaware and New York. Justice Department officials have pledged to colleagues that they will arrest those who vandalized the Capitol. The active-duty military hasn’t been deployed and shouldn’t be needed.

Appalled Trump administration officials are jumping the sinking ship, but they shouldn’t overdo it. I hope that national security adviser Robert C. O’Brien stays in place, for example. Someone must help Pence prevent Trump from carrying out any reckless orders.

Thinking about Wednesday’s events, it’s useful to indulge in what Harvard professor Ernest May liked to call “Applied History.” What if the situation had turned out differently — and force had been used more aggressively, as in past efforts to deal with civil strife? We can think of some obvious examples: Police brutality against Chicago street protests during the 1968 Democratic convention gave new energy to the Vietnam antiwar movement; so did the tear-gassing and mass arrests during the 1970 “May Day” protests. Police overreaction to unrest following Rodney King’s death left a permanent stain on Los Angeles.

The 1989 Tiananmen Square massacre is an extreme example. The Trump anarchists don’t deserve comparison to the brave Chinese pro-democracy activists. But they wanted similar images of a brutal government crackdown, even martyrdom, that could have energized their movement for years.

Trump’s fanatical followers didn’t get their wish. Instead, they got what they deserved — public revulsion and failure.

This column has been updated.

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