Iraqi youth watch the news of the ISIS leader Abu Bakr al-Baghdadi's death.Alaa al-Marjani / Reuters

In the Syrian rebel’s telling, he’d encountered Abu Bakr al-Baghdadi without even realizing it.

It was early in Syria’s civil war, he explained, before the Islamic State surged to global notoriety. The jihadist group was then still in a tenuous partnership with rebel groups such as his in an insurgency against the Bashar al-Assad regime. During occasional meetings with ISIS leaders, the rebel said, he’d noticed a quiet man who seemed to be something like a secretary. This man would serve the guests tea, then blend into the background. Only later, when the man became infamous as the world’s most wanted terrorist, did the rebel recognize him as Baghdadi.

I heard this story in the chaotic early days of the U.S. war against ISIS and never confirmed it—instead, I considered it a wartime yarn that spoke to a larger truth about Baghdadi and the group he led. The rebel’s story captured the way Baghdadi and ISIS were understood by many of their enemies: as shadowy, lurking, difficult to grasp.

ISIS was so effective at taking and maintaining control in Iraq and Syria because it operated so well in the shadows. The same calculating instincts attributed to Baghdadi in the rebel’s tale—in which the ISIS leader was apparently shrewd enough to mask his identity from his rebel allies, knowing that he would one day turn on them—helped ISIS establish a stranglehold over a large swath of territory. The same combination of careful planning and unrelenting treachery was integral to the extremist group’s rise. Its early territorial victories in Syria were not taken from Assad, but from rebel groups. And these were not opportunistic victories born from the chaos of war. As the journalist Christoph Reuter has documented, ISIS first compiled dossiers on the locals it intended to kill or co-opt: lists of powerful families and their sources of income, the names and political orientations of rebel leaders, information that could be used for blackmail. Then it would make its move.

Similar efforts preceded ISIS’s seizure of Mosul and parts of Anbar province across the border in Iraq; the months before the ISIS surge were marked by assassinations. “They have agents and spies everywhere,” an Iraqi military officer, an Anbar native, told me from hiding in the summer of 2014, explaining that ISIS knew the names, ranks, home addresses, and salaries of police officers and soldiers throughout the areas it had recently seized.

From there, ISIS used a reign of terror to keep millions of Syrians and Iraqis in its clutches. It claimed them as citizens of its hard-line state, but in reality they were hostages. The way most Syrians and Iraqis experienced the group was as a brutally effective intelligence agency. Neighbors informed on one another; dissent was punished. Even in southern Turkey, where I met the rebel commander in question, Syrians were afraid to discuss the group, wary of retribution. Conversations about ISIS in the region’s hotels and cafés were hushed and nervous, as people worried about—even in Turkey, a NATO member state—who might be listening. Just as in Syria and Iraq, ISIS had established underground cells throughout the country.

The shadowy, lurking aspect of Baghdadi also defined his image internationally. He gave just a single public speech: a sermon in Mosul’s Great Mosque of al-Nuri in July 2014, during which he claimed the restoration of the caliphate, an idea that was an abomination to all but a tiny fraction of the world’s 1.8 billion Muslims. Citizens of Europe, the United States, and other places that were subject to Baghdadi’s terrorist ambitions experienced him less as the self-styled Caliph Ibrahim than as a purveyor of murky, senseless violence.

Where Osama bin Laden focused his efforts on spectacular attacks, Baghdadi stood out for promoting the idea that any sort of violence would do. ISIS carried out horrific mass-casualty attacks: killing more than 100 in Ankara in October 2015 and in Paris the following month, as well as dozens more in Brussels in March 2016, in Istanbul in January 2017, and in Manchester in May 2017. It also carried out an endless series of lower-grade atrocities: stabbing passersby, driving vehicles into crowds. And it encouraged lone wolves, such as the Orlando, Florida, nightclub shooter, to carry out attacks in its name.

The sum of all this was to promote the idea that anyone could be a threat. It was designed to make people suspicious of their neighbors, or of newly arrived refugees. It pitted people against one another.

This is worth remembering as Donald Trump takes credit for Baghdadi’s death, because Trump himself helped advance this part of Baghdadi’s cause. As the journalist Murtaza Hussain argued in the wake of the Paris attacks, ISIS was seeking to eliminate what it called the “gray zone” of co-existence between Muslims and the West. “By launching increasingly shocking attacks against Western targets, the Islamic State is pursuing a specific goal—generating hostility between domestic Muslim populations and the broader societies that they live in,” Hussain wrote. “[It] is consciously seeking to trigger a backlash by Western governments and citizens against the Muslim minorities living in their societies. By achieving this, the group hopes to polarize both sides against each other, locking them into an escalating spiral of alienation, hatred and collective retribution.”

The month after the attacks in Paris, Trump, then a presidential candidate, made his first call for a so-called Muslim ban.

In his remarks about Baghdadi’s killing yesterday, Trump boasted that it was more important than Bin Laden’s had been. But he appeared to miss a key distinction: Baghdadi’s penchant for operating in the shadows made him a less important figure to the group he led. Bin Laden was always a far more effective front man—both to his followers and to his enemies. He founded al-Qaeda; though Baghdadi was ISIS’s leader when it declared itself to the world, the group derived itself from al-Qaeda in Iraq, which was founded by the Jordanian Abu Musab al-Zarqawi. After Baghdadi’s rise to fame, he seldom emerged from hiding, prompting regular speculation that he was dead. He was widely believed to have given up operational control of the group years ago. While bin Laden loomed large in the minds of Americans in the years following the September 11 attacks, Baghdadi’s effect was more diffuse: He channeled his brand of utilitarian cynicism to a loosely affiliated network of global supporters. As a result, his impact will be harder to snuff out with his death.

ISIS also retains its innate ability to operate in the shadows. Having lost its territory, it has returned to its roots as an underground insurgency. The New York Times reported this summer that ISIS has as many as 18,000 fighters across Syria and Iraq, most of them in hiding. Rolling up these networks is exactly the work that the U.S. troops who were based in Syria—and their Kurdish partners—were busy doing. Trump’s ill-planned withdrawal has badly undermined these efforts, offering ISIS a lifeline. In his remarks, Trump thanked first Russia and then Turkey, the two countries with which he has aligned in his chaotic recent moves in Syria. Yet both have spotty track records in combatting ISIS, and news accounts have since confirmed the obvious: that Syrian Kurds, whom Trump thanked last, helped the U.S. collect valuable intelligence that led to Baghdadi. The Kurds reportedly continued to assist in this effort even after Trump’s withdrawal cast them into a dangerous limbo.

Baghdadi’s death, and the demise of his so-called caliphate, shouldn’t be underestimated. That ISIS controlled a hard-line state, and could offer recruits the chance to live its nihilist vision, was integral to what made it such a radical sensation, and was key to Baghdadi’s recruiting power. Now both the caliph and the caliphate are gone. Yet ISIS survives underground, lurking in the shadowy manner Baghdadi helped to define for it.

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