In a country starved for good news, we should be celebrating the fact that, after Sept. 11, 2001, we’ve gone 10 years without a major follow-up attack on American soil.

But some folks just refuse to be cheered up. At last week’s GOP debate, Newt Gingrich helpfully reminded everyone that “there are people out there who want to kill us.” Therefore, we need a Department of Homeland Security with the “capacity to respond to massive events that could kill hundreds of thousands of Americans in one morning.”

That’s a tall order for an institution whose core competence seems to be groping preschoolers on security lines.

More to the point, is there any evidence at all that that’s the magnitude of the threat we’re facing?

Last month’s rough weather provoked some debate over whether the government overreacted to Hurricane Irene. But Irene killed more Americans in one weekend than jihadists have managed in a decade. Irene’s death toll stands at 44; Islamic radicals in the U.S. — even counting the Beltway snipers, who looked more like random lunatics than al Qaeda operatives — have killed just over 30 since 9/11.

Every one of those deaths is a tragedy, an outrage, and a crime. Yet since 9/11, more than twice as many have died in what the FBI classifies as “hate crimes,” and in a typical year more Americans die in random shootings than terrorist attacks. When incidents like the Columbine and Virginia Tech massacres happen, most of us rightly resist the idea that we need to start jettisoning constitutional liberties to protect ourselves.

Is it government policy that’s kept us safe? To some degree, sure. We’ve put great pressure on al Qaeda’s core leadership abroad, disrupting its ability to plot and raise funds.

But there’s good reason to believe the al Qaeda threat was never as “existential” as it was cracked up to be.

In 9/​11’s aftermath, FBI officials warned that there might be as many as 5,000 al Qaeda operatives within the United States. FBI Director Robert Mueller insisted that the group had “developed a support infrastructure” with “the ability and the intent to inflict significant casualties in the U.S. with little warning.”

Yet in 2005, ABC News obtained a classified FBI report admitting that in a country supposedly honeycombed with al Qaeda operatives, they couldn’t find any. “To date,” the report stated, “we have not identified any true ‘sleeper’ agents in the U.S.”

Not much has changed in the six years since that memo.

Last week, RAND Corp. published a study looking at homegrown jihadi terrorism. Of the 32 “plots” uncovered in the U.S. since 9/11, “only 10 developed anything resembling an operational plan that identified a specific target, developed the means of attack, and offered a sequence of steps to carry [it] out.” “Of these, six were Federal Bureau of Investigation stings” involving fake bombs — “on their own, only two individuals actually attempted to build devices. One was arrested while doing so, and the other’s device failed.”

The RAND report sums up: “Thus far, despite al Qaeda’s intensive online recruiting campaign, their numbers remain small, their determination limp, and their competence poor.”

In May 2010, after the Times Square bomber’s jerry-rigged contraption of gas cans, firecrackers and fertilizer ruined his Pathfinder’s upholstery, Attorney General Eric Holder proclaimed “the most dangerous impression we can draw is that this threat no longer exists.”

But by convincing ourselves that the threat is “existential,” we’ve wasted trillions and built a surveillance state that refuses to recede with the waning al Qaeda threat. Complacency can be dangerous, but it’s hardly the only danger.