On March 19, citing the virus, coalition and NATO training missions both suspended operations for two months. By March 29, Australia, Spain, France, the United Kingdom, New Zealand, Portugal and the Netherlands had withdrawn almost all of their trainers.

In parallel, the U.S. withdrew from its frontline operating bases at Mosul, Al-Qaim, Qayyarah, Kirkuk and Taqaddum in the last week of March. Most U.S. forces were redistributed inside fewer, better-protected Iraqi bases such as Al-Asad and Erbil airport, both of which are now protected by newly installed U.S. missile defenses, to prevent a recurrence of the Jan. 8 Iranian missile attacks that left more than 100 U.S. troops with mild traumatic brain injuries.

The Iraqi military are meanwhile distracted by disaster relief, enforcing a nationwide curfew, and looking after their own health and that of their families. (Officially, the virus had sickened over 1,100 and killed 65 Iraqis as of Tuesday, but lack of testing means the real number is likely significantly higher.) Rural clearance operations have almost ceased and the pace of special forces raids has slackened, in part because of the severe disruption to intelligence, planning and air support provided by the U.S.-led coalition.

For the Islamic State, this is all a godsend. In its view, the pandemic is a literal act of divine intervention as it reached its lowest ebb. Terrorism expert Aymenn Jawad al-Tamimi noted that IS’ newsletter, Al-Naba, called coronavirus “God’s torment” upon the “Crusader nations,” and urged fighters to take advantage of the distraction and disruption caused by the virus.

In many ways the Islamic State is quite well adapted for operations during a pandemic. Its cells are isolated, avoiding the risk of contamination by performing extreme social distancing long before the rest of us. Its leadership issued early instructions to its cadres to limit their exposure to the virus—from the CDC-approved recommendations (washing hands and “covering up” coughs and sneezes) to Koranic verses involving lions and leprosy.

IS are somewhat self-contained, living in remote hideouts and underground shelters, drawing on independent food and water caches, and powering electronic devices with solar battery chargers. In every sense of the phrase, the thousands of members of this millenarian terrorist cult are the ultimate doomsday preppers.

On the ground, there have been small signs of Islamic State recovery at the tactical level, probably due to the cessation of counterinsurgency operations targeting them.

The four Iraqi military “clearance” operations undertaken in March were half as many as in April, and they lacked the coalition intelligence and air support that can focus such operations more effectively, instead falling into the less efficient category of unearthing arms caches but not catching enemy fighters.

Whereas U.S. and Iraqi special operations forces did a minisurge of joint raids in February—dropping in by U.S. helicopters or tilt-rotor Osprey aircraft to raid caves and stop vehicles driven by IS members—there were no such raids in March.

Left to operate without being pressured and chased from hideout to hideout, Islamic State has been getting more ambitious at local level. In Khanaqin District, close to the Iran-Iraq border, IS quadrupled its average number of mortar and rocket attacks in March and combined the bombardments with sustained machine-gun fire and ground assaults on security force outposts.

Over a five-day period beginning March 17, insurgents fired 15 mortar rounds into heavily populated neighborhoods of cities such as Tuz Khurmatu and Amerli, a type of attack that has not been seen for more than two years.

Islamic State’s next steps are easy to guess. It will increase rural assassination raids on local village leaders—so-called mukhtars—and use intimidation to increase its ability to raise funds. Disruption to security force clearance operations will increase IS’ ability to make advanced roadside bombs in its hideouts and use these weapons, and other harassment tactics, to keep the security forces buttoned down in their bases.

If left unchecked, this kind of aggressive patrolling allows insurgents to gain psychological dominance over the local military garrisons and civilian populations. Before long, the insurgents will become the local power brokers, and it will no longer be possible to claim that IS’ days of territorial control are over. This is how the caliphate knits itself back together, one village at a time. This is exactly how it happened in 2012-14, after the previous U.S. withdrawal.

The only way to stop an IS resurgence, still in its infancy but now facing an improved outlook, is to reinvigorate an effective counterterrorism raiding campaign. This requires ongoing partnership between U.S. and Iraqi special forces, and between Iraq’s commandos and the local Sunni populations in IS strongholds. Unlike 2011, the U.S. should not leave Iraq entirely, but should rather lower its visibility.

In all likelihood, non-U.S. military forces will never return to Iraq in the numbers that were recently withdrawn, with the virus providing a way to justify withdrawal even though Iraqi security forces are arguably not prepared to restrain an Islamic State resurgence. U.S. forces may also dwindle in terms of raw numbers in Iraq, where Iran-backed factions are promising long-term armed resistance to the open presence of U.S. advisers.

This does not have to be the end of an effective counterterrorism fight, however.

In places as diverse as Yemen, Somalia, Mali and Syria, the U.S. Special Operations Command has employed quiet partnerships with local special forces and paramilitary proxies to take on terrorist cells in a more targeted and effective manner than the large-scale train-and-equip program that appears to be eroding in Iraq. The coalition mission in Iraq—due to turn 6 years old in September—might expire, but the effort to prevent another IS comeback cannot afford to take a break, whether as a result of coronavirus, Iran-backed militias or a devilish combination of the two. The answer may be to take the war underground and back into the shadows.