The scene outside Marjory Stoneman Douglas High School in Parkland, Florida following this week's school shootingZachary Fagenson / Reuters

Upon learning of the murder of 17 people at a Florida high school on Wednesday, the activist Michael Skolnik reissued a plea for gun-control measures that he’s made in the wake of previous mass shootings. “One shoe bomber tried to blow up a plane and now we are forced to take off our shoes,” he wrote on Twitter, in reference to airport-security policies implemented after a terrorist attempted to detonate explosives in his shoes on a Miami-bound flight in 2001. “1606 mass shootings since Sandy Hook Elementary School and Congress has done NOTHING.” The academic Brian Klaas expressed a similar sentiment: “After 9/11, we reinforced cockpit doors & tightened security. We didn’t say ‘the only thing that stops a hijacker is a good guy on a plane.’”

Setting aside the fact that we did put good guys with guns (air marshals) on planes to stop hijackers, these arguments actually immensely understate the U.S. government’s response to terrorism since the September 11 attacks.

The United States launched a war in Afghanistan and various far-flung counterterrorism operations against al-Qaeda and its successors that, 16 years later, with no end in sight, have cost hundreds of billions—depending on how you count, perhaps trillions—of dollars. The U.S. Congress approved or signed into law four dozen 9/11-related bills and resolutions in the year after the attacks, including an authorization for the American president to use force against al-Qaeda that has mutated into blanket permission for the commander in chief to take military action against anything resembling a terrorist anywhere in the world.

America has created or reshuffled more than 260 government organizations since the 9/11 attacks, including massive new entities such as the Department of Homeland Security and the Office of the Director of National Intelligence. It has poured hundreds of billions of dollars into securing the homeland, from $1 million baggage-screening machines to a failed $1 billion camera-and-sensor network at the U.S.-Mexico border. It has invested vast sums in more intrusive surveillance activities and other means of intelligence gathering—precisely how vast, no one can say. The covert world fashioned by U.S. leaders after 9/11 “has become so large, so unwieldy, and so secretive that no one knows how much money it costs, how many people it employs, how many programs exist within it, or exactly how many agencies do the same work,” The Washington Post reported in 2010.

Terrorist attacks and mass shootings are distinct phenomena—though, as in the 2016 Orlando nightclub shooting, they occasionally overlap. (One in five terrorist attacks in the United States between 2002 and 2016 involved firearms.) Terrorism is typically directed or inspired by specific organizations that serially practice violence for political ends and that attack not just individuals but society. It’s therefore challenging to compare with mass shootings, whose damage is usually measured in casualty counts and which can have a range of motivations. But both are rare yet recurring, terrifying, and to a considerable extent preventable acts of mass destruction. And even if you add all the caveats you want to the statistics showing that the number of Americans killed by terrorism in the post-9/11 period is a fraction of the number of Americans killed by mass shootings, it’s hard to avoid one conclusion: In terms of action and investment, there is a colossal gap in how the U.S. federal government has prioritized stopping one form of aberrant violence versus the other.

While efforts to reform gun laws have made progress in a number of U.S. states, they’ve repeatedly stalled in Congress in recent years. The U.S. government spends roughly $22 million a year on gun-violence research—a “tiny fraction of what it spends on other major health threats,” according to NPR. It’s an even tinier fraction of what it spends on counterterrorism; we’re talking the equivalent of 22 baggage-screening machines. Even when Barack Obama, a staunch gun-control advocate, asked Congress for more money to counter gun violence, his requests were in the low billions of dollars.

These differences stem in large part from the disparate ways that terrorism and gun violence are perceived and experienced in the United States. While U.S. mass shootings took 117 lives in 2017 alone by one count, they haven’t caused the all-at-once devastation of 9/11, which killed nearly 3,000 people. America has not witnessed a terrorist attack on that scale since then, but U.S. policymakers remain focused on making sure one never happens again. The September 11 attacks left an enduring (if outdated) impression of counterterrorism as an exercise in going after definable overseas targets, whereas gun restrictions alarm those concerned about the government going after Americans and their constitutional rights.

There is, of course, a case to be made that the United States has gone much too far in trying to avert terrorism. Several months ago, for example, Donald Trump fumed when his advisers pressed him to deploy more forces to Afghanistan and escalate the fight against ISIS affiliates in North Africa. “You guys want me to send troops everywhere,” Trump said, according to The Washington Post’s account of the meeting. “What’s the justification?” Defense Secretary James Mattis reportedly replied: “Sir, we’re doing it to prevent a bomb from going off in Times Square.”

But when massacres like the one in Florida occur, that kind of justification raises a profoundly troubling question: Why has the government done so little to prevent a gun from going off in the nation’s schools?