Abu Bakr al-Baghdadi was, as President Trump said, “a sick and depraved man,” so his removal from this earth is good news. The operation to kill him attests to the superlative skills of the U.S. Joint Special Operations Command and, yes, the U.S. intelligence community. Our intelligence officers are, as Trump said Sunday, “great” professionals, not part of a deep state out to undermine him, as he so often suggests. This operation was no more Trump’s doing than the death of Osama bin Laden was President Barack Obama’s. (Trump tweet from 2012: “Stop congratulating Obama for killing Bin Laden. The Navy Seals killed Bin Laden.”) But both men approved the risky operations and can bask in their reflected glory.

However, I have sat in too many U.S. military headquarters in Iraq and Afghanistan over the past two decades listening to Special Operations officers announce “jackpots” — the killing or capture of “high value targets” — to imagine that any such success will translate into final victory over their organizations. To be sure, some terrorist and guerrilla groups that were already on the wane have suffered severe blows from the loss of their leaders. This was the case with the Philippine insurrectos fighting U.S. rule when the rebel leader Emilio Aguinaldo was captured in 1901 and with the Shining Path in Peru when its leader Abimael Guzman was captured in 1992.

But, as I argued in my 2013 book “Invisible Armies: An Epic History of Guerrilla Warfare from Ancient Times to the Present,” “Decapitation strategies work best when a movement is weak organizationally and focused around a cult of personality. Even then leadership targeting is most effective if integrated into a broader counterinsurgency effort designed to separate the insurgents from the population. If conducted in isolation, leadership raids are about as effective as mowing the lawn; the targeted organization can usually regenerate itself.”

Recent history offers numerous examples to illustrate this thesis. Abbas al-Musawi, the secretary general of Hezbollah, was killed by the Israel Defense Forces in 1992, only to be succeeded by Hasan Nasrallah, who has made this Iranian-backed organization far more powerful than ever. Abdullah Ocalan, the leader of the Kurdistan Workers’ Party (PKK), was captured by Turkish forces in 1999, and yet the threat of Kurdish separatism remains so strong, at least in the mind of Turkish President Recep Tayyip Erdogan, that he used it to justify his recent invasion of northern Syria. Akhtar Mohammad Mansour, the leader of the Taliban, was killed in a U.S. drone strike in 2016, but the Taliban remains undefeated.

More to the point, Abu Musab al-Zarqawi, the leader of al-Qaeda in Iraq, was killed in a U.S. airstrike in 2006, and yet the security situation in Iraq continued to spiral out of control until the “surge” — a shorthand for a comprehensive counterinsurgency plan implemented in 2007 by Gen. David H. Petraeus. Even after al-Qaeda in Iraq was all but defeated, it managed to spring from the grave following the pullout of U.S. forces from Iraq in 2011. It was reconstituted as the Islamic State under the leadership of the now-deceased Baghdadi.

There is every reason to fear that Islamic State now could prove distressingly resilient despite this monster’s death. This summer, inspectors general from the Defense and State departments and the U.S. Agency for International Development warned that Islamic State retained as many as 18,000 fighters in Syria and Iraq and was starting to stage a comeback. That resurgence is likely to be accelerated by Trump’s ill-advised pullout from northern Syria, which ends a partnership with the Kurds that, among other benefits, provided intelligence that contributed to the track-down of Baghdadi. Trump is now dismantling the infrastructure that made this success possible.

Defense Secretary Mark T. Esper admitted that more than 100 Islamic State detainees have already escaped — and there is no evidence to back up Trump’s boast that they have been “largely recaptured.” Terrorist organizations flourish in a lawless environment, and the end of the U.S. partnership with the Kurds will contribute to the chaos in eastern Syria, despite Trump’s puzzling decision to secure Syria’s tiny oil fields. Turkish and Russian forces have neither the capability nor incentive to take over the U.S. counterterrorism mission. Indeed, Turkey looked the other way for years as foreign jihadists transited its territory to join Islamic State in Syria.

What’s true of Syria is true of other battlefields in the global war against terrorism. A report from the Center for Strategic and International Studies last year found: “Despite nearly two decades of U.S.-led counterterrorism operations, there are nearly four times as many Sunni Islamic militants today as there were on September 11, 2001. … The regions with the largest number of fighters are Syria (between 43,650 and 70,550 fighters), Afghanistan (between 27,000 and 64,060), Paki­stan (between 17,900 and 39,540), Iraq (between 10,000 and 15,000), Nigeria (between 3,450 and 6,900), and Somalia (between 3,095 and 7,240).”

The only way to permanently defeat terrorist organizations is to foster stability in the lands where they operate — the last thing that Trump, an agent of instability, is interested in. By removing most U.S. troops from Syria, and soon perhaps Afghanistan, he is likely to hand a victory to the terrorists that will far outweigh the transitory effects of Baghdadi’s demise.

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