In April, President Obama called his 2011 intervention in Libya the “worst mistake” of his presidency, and it’s not a bad candidate for the title. But beyond any one specific conflict, Obama’s tenure has been closely tied to a tactic—drone warfare—which is at least in the running for second place in this administration’s panoply of foreign policy errors.

Though weaponized U.S. drone use began under former President George W. Bush, it was with Obama that the model really came into its own, both numerically and in the national conversation. Once shocking for their mechanized, even trivialized killing technique—who can forget the 2012 “kill list” story, which saw Obama using grotesque ‘baseball cards’ to handpick people for assassination by robot?—drone strikes today have become routine. The White House insistently describes the practice as surgical targeting, claiming just this month (over the many protests of independent watchdogs) that accidental civilian deaths are negligible.

Indeed, to the extent that debate about drone use lingers, it typically focuses “on its legality and morality, while its effectiveness as a counterterrorism strategy has gone largely unquestioned,” explains Emily Manna in a new analysis published at the Georgetown Public Policy Review. Manna’s research questioned the widespread assumption—a belief Washington seems only too happy to foster—that drone warfare, whatever other objections some may raise, is valuable tool in the war on terror.

Her report suggests that assumption is deeply false. In fact, looking at the incidence of terrorism in parts of Pakistan hit with U.S. drone strikes from 2006 to 2012, Manna discovered that terrorist activity actually increased in a province after it was subjected to drone warfare.

As noted by FBI Director James Comey, “At some point there is going to be a terrorist diaspora out of Syria like we’ve never seen before. Not all of the Islamic State killers are going to die on the battlefield,” and thanks in significant part to the hatred fostered by drones, their numbers will not be few. Comey’s warning can be applied more broadly to U.S. interventionism, and specifically drone warfare, which has served to destabilize the region and create power vacuums that allow terrorism to thrive.

As Ret. Gen. Stanley McChrystal warned to apparently deaf ears in 2013, drone warfare engenders a unique animosity among Mideast civilians, which few in Washington seem to understand. “What scares me about drone strikes is how they are perceived around the world,” said McChrystal, who designed U.S. counterinsurgency strategy for Afghanistan. “The resentment created by American use of unmanned strikes ... is much greater than the average American appreciates,” he added. “They are hated on a visceral level, even by people who’ve never seen one or seen the effects of one.”

Jillian Schwedler, an American political scientist who has traveled extensively in the Middle East, has reported similar observations. For al-Qaida in Yemen, “the drone program is a gift from the heavens,” she said. “It provides evidence that al-Qaida’s claims and strategies are justified … and embitter[s] Yemenis who might otherwise be neutral.” In other words, Obama’s drone warfare is making more terrorists than it kills.

That’s the sort of detail that ought to give anyone serious about stopping the tide of terrorism sober pause.

Of course, drone strikes were always more about convenience than effectiveness, as CIA veteran Paul Pillar wrote while reviewing Manna’s research. “But if the result of a tactic—in counterterrorism or any other endeavor—is a net minus rather than a net plus,” Pillar reasoned, it is foolish at best to cling to its use. Because this is a question of counterterrorism, maintaining Obama’s drone war becomes outright dangerous to U.S. security. To be sure, the president is unlikely to admit the failure of his signature tactic before he leaves office in January, but for the next president, a reexamination of our drone war’s effectiveness should be at the top of the to-do list.