This week, a mob of extremists, incited by President Donald Trump, bypassed police lines and entered the Capitol. They smashed windows and furniture, stole a lectern and laptops, and broke into the Senate chambers. They disrupted Congress and forced lawmakers to evacuate to security bunkers. Five people died, including a Capitol Police officer, and about 50 other officers were injured. Three bombs were found on the Capitol grounds and at the Democratic and Republican national headquarters.

This insurrection revealed a shocking lack of security: The system meant to keep order at the seat of American democracy plainly failed. The rioters did not pass through metal detectors or any sort of security apparatus on their way into the building, and many seemed to be armed. One man was found to be carrying 11 Molotov cocktails “ready to go,” according to the Department of Justice. Officers arrested only about 20 rioters during the siege, allowing most of them to walk out of the Capitol as if they had done nothing wrong, and an officer may have even directed rioters toward the office of Senate Minority Leader Chuck Schumer when asked, according to The New York Times.

A breach such as this will have consequences. The chief of the Capitol Police has already resigned, as have the House and Senate’s chief law-enforcement officers. Congress must hold an inquiry to understand what happened and how the building could have been invaded. Hundreds of millions of dollars of post-9/11 security improvements did not prove sufficient to keep a few thousand people from storming the gates. Americans must understand, too, why the Capitol Police repeatedly turned down offers for reinforcements on the days leading up to the riot and during the invasion itself. This cannot happen again. We must have answers.

[Read: The inaction of Capitol Police was by design]

Yet getting those answers must be understood as necessary, but not sufficient, to prevent whatever happened this week from happening again. The question “How can we secure the Capitol?” is the means by which this week’s catastrophe will be blunted. One can already imagine the speeches: Whether you think pro-Trump loyalists or antifa broke into the Capitol, we can agree that the seat of our national government must be better protected, a lawmaker will say, on the verge of voting for a big, bipartisan bill to buy more roadblocks. Members of Congress have already started down this path. “U.S. Capitol security needs a total overhaul. The physical breaching and desecration of our temple of democracy must never happen again,” Senator Brian Schatz, a Democrat from Hawaii, said on Twitter. The thing is, he is right, but physical security improvements alone will not protect the Capitol from another insurrection.

Because, really, no amount of security paraphernalia can prevent what happened this week from happening again. The head of the executive branch incited a group of armed supporters to attack the legislative branch. It is impossible to protect the Capitol against such a threat with more barricades and officers. I don’t just mean that this sort of reinforcement is difficult; I mean that it is impossible: Congress will never be able to muster the same weapons available to the president. You can design a legislative complex to withstand many threats, but warfare among the co-equal branches is not one of them. The government cannot be a fortress against itself.

So the response to this week’s insurrection cannot merely be about the physical security of the Capitol building. The acquisition of new weapons and barriers must not be our primary response to the siege. The Capitol grounds themselves are gloriously open to the public. Any person can wander through the same gardens as a senator. The Capitol complex—the dozen-plus buildings that comprise the House and Senate offices and the Library of Congress—is the last seat of federal power that any American can enter without an appointment. (The Capitol itself requires more planning to enter, but it is open to the public in a way that the White House is not.) It is a crowded, egalitarian mecca, where on any average Tuesday you can see unionized nurses, men in cowboy hats, uniformed military officers, and gawking tourists. It is one of the final working public places in Washington. To protect its status as a monument to democracy, we must not sacrifice what actually makes it democratic.