President Donald Trump backed up last week’s reckless decision to withdraw the U.S. military from Syria by claiming that the Islamic State of Iraq and the Levant (ISIL) has been defeated in Syria. His advisors disagree . It appears the president didn’t get the memo. Or maybe he did — given that he later contradicted himself, claiming ISIL was other countries’ problem now — and just chose to ignore it. Either way, hastily withdrawing U.S. forces from Syria will have numerous negative consequences for the United States, its allies, and partners in the region.

First and foremost, cutting and running from Syria will breathe new life into ISIL and could benefit al-Qaeda’s operations in the area as well. U.S. forces have put direct pressure on militants from both groups, and also played a critical role in supporting other actors on the ground fighting against them. In addition, without the military’s logistical support, U.S. intelligence agencies will face a much harder time collecting intelligence on the ground in Syria. This will make it much more difficult for the United States and its Western allies to detect external operations planning by ISIL or al-Qaeda. Abandoning the Syrian Democratic Forces (SDF), America’s main partner on the ground, will also weaken the coalition that is helping fight ISIL and could lead coalition members to curtail or end their efforts in this area entirely. Second, pulling out of Syria in such a sudden manner will embolden Iran and Hizballah. The presence of U.S. forces has served as a check on their activities, and is key to pushing back on Iranian adventurism across the region. In addition to the direct loss of pressure on Tehran, the exit of U.S. forces is very likely to create a vacuum and with it greater competition for the territory currently controlled by the U.S.-supported SDF. Regional power brokers, including Iran, its client, Syria, and Turkey, will benefit by filling the void.

Countering ISIL

The president’s decision to declare victory in Syria and pull out U.S. forces recalls the mistakes that Presidents Bush and Obama made by underestimating earlier ISIL iterations. After Bush declared “Mission Accomplished” in May 2003, Jama’at al-Tawhid wa-l-Jihad, which was led at the time by Abu Mu’sab al-Zarqawi, was on its way to becoming the dominant insurgent faction against U.S. forces. It was renamed al-Qaeda in Iraq a year later when al-Zarqawi pledged an oath of allegiance to Osama bin Laden. Al-Qaeda in Iraq rebranded itself as the Islamic State of Iraq in 2006, and expanded to become the Islamic State of Iraq and the Levant in January 2014. Obama’s derisive labeling of ISIL that same month as the “J.V. Squad,” in comparison to al-Qaeda, occurred merely six months before the group seized territory the size of Britain spanning parts of Iraq and Syria. Trump’s abrupt withdrawal suggests a similar overconfidence. Yet it is arguably worse. Bush made his speech before the jihadist threat had manifested, and Obama’s gaffe occurred prior to its resurgence. Where his predecessors failed to take a looming threat seriously enough, Trump is taking his eye off the ball and pulling the United States out of the game before the current iteration of ISIL is defeated.

Trump’s top counterterrorism advisors do not share his overconfidence. Vice Adm. Joseph Maguire, who was finally confirmed as the new director of the National Counterterrorism Center, testified earlier this year that despite losing most of its territory, ISIL’s “ability to launch an insurgency in Syria and Iraq and maintain a global network has not yet been sufficiently diminished, and the consistent tempo of ISIL-directed and ISIL-inspired terrorist activity is a reminder of the group’s continued global reach.” U.S. government agencies have not altered their assessment since Maguire’s testimony. A week before Trump announced the hasty withdrawal, Brett McGurk, the special presidential envoy for the global coalition to defeat ISIL, said, “ Nobody is declaring mission accomplished .” McGurk has since resigned in protest over the president’s decision. And a day before Trump tweeted an end to the military mission in Syria, his special representative for Syria engagement, Amb. Jim Jeffrey, reiterated the need to maintain a U.S. military presence in Syria to secure the enduring defeat of ISIL, pressure Iranian-commanded forces to withdraw from the country, and contribute to conditions for a political resolution to the civil war in order to help stabilize the region.

There is plenty of empirical evidence to support the concerns that Trump’s own advisors have voiced. Earlier this year, the United Nations released a report suggesting that ISIL still had up to 20,000 to 30,000 fighters in Iraq and Syria. On December 19, a spokesman for the American-led coalition against ISIL, Col. Sean J. Ryan, estimated that the group still had 2,000 to 2,500 fighters just in Hajin, ISIL’s last territorial stronghold in Syria. Even if Hajin was taken earlier this week, assessing that ISIL has been defeated based on territorial control would repeat analytical errors and underestimate the group’s ability to rebound in the same way that many took the success of the surge and tribal awakening from 2007 to 2010 as working. Although ISIL has not controlled territory in Iraq for more than a year, the group has reestablished its insurgent capacities, raising the level of violence in Kirkuk, Ninawa, and Diyala provinces. ISIL today has successfully followed the same playbook it did following the surge and tribal awakening, by killing local leaders and town elders to gut any chance that areas they had once controlled could become stable and rebuilt. Furthermore, despite controlling almost no territory in Syria, ISIL carried out a series of attacks in al-Raqqa and Deir al-Zour provinces and claimed them via Telegram within hours of Trump’s announcement. On top of this, ISIL has continued to build up sleeper cell capacities in Idlib province to try and wrest control of the area from competing jihadi groups like Hayat Tahrir al-Sham.

A withdrawal will also affect U.S. partners fighting ISIL. Within hours of the president’s tweet, reports emerged that the U.S.-allied, Kurdish-dominated Syrian Democratic Forces — who would be abandoned in Northeast Syria when U.S. forces withdraw — were considering releasing up to 3,200 ISIL prisoners they were holding. Most of these individuals are foreign fighters. Releasing them could present immediate threats to European and other countries, including possibly the United States. As the Trump administration’s own National Security Strategy observes, “ Many of these jihadist terrorists [in Iraq and Syria] are likely to return to their home countries, from which they can continue to plot and launch attacks on the United States and our allies.” It is also worth remembering that prison releases from 2010 to 2014 contributed to ISIL’s resurgence capability.

Against this backdrop, as well as reports that the U.S. withdrawal could include an end to U.S. airstrikes as well, key allies including France and the United Kingdom issued statements underscoring their assessments that despite losing significant territory ISIL is not defeated and remains a threat. Yet it is highly questionable whether either of these countries will remain engaged in the region to the same degree if the United States withdraws. There withdrawal would not only be a further blow to the anti-ISIL campaign and to regional stability, but also to the wider U.S. effort to promote burden sharing.

Outside Iraq and Syria, ISIL continues to inspire individuals to kill in its name. Earlier this week, four men who pledged allegiance to Abu Bakr al-Baghdadi beheaded two female tourists in Morocco while they were hiking and camping. In a prerecorded video, they tied the attack to events in Syria, saying, “this is in revenge for our brothers in Hajin.” If ISIL is able to regain its territorial control it will have far more resources and assets without pressure to plan more sophisticated attacks like its most notorious one in Paris in November 2015. In other words, ISIL poses a multi-layered threat that transcends the boundaries of whatever limited territory it operates in Iraq and Syria. ISIL remains a capable terrorist and insurgent threat in the region and beyond, including its far-flung branches in places like Afghanistan, Egypt, Somalia, and the Philippines. Withdrawing troops and stopping the air campaign against the organization will only embolden them and set the stage for another comeback locally and internationally.

Iran Threat Network

Besides defeating ISIL, the Trump administration has also made countering Iran’s state sponsorship of terrorism a priority, including in both its national security and counterterrorism strategies. As Amb. Jeffrey explained in November, the U.S. military presence in Syria helps to curtail Iran’s malign activities. It prevents Iran from securing a land bridge to Lebanon, across which it could more easily arm Assad and Hizballah with rockets and other weapons, and complicates Iranian efforts to build an “ expeditionary force ” from the battle-hardened Shiite militias it has built and backed in Syria and Iraq. “We’ve seen firsthand in recent months how dangerous these proxies can be,” the State Department counterterrorism coordinator recently commented , pointing out the rockets launched at the U.S. embassy in Baghdad and consulate in Basra were by Iraqi Shia militias tied to Iran. Thus, it is clear that Iran and its proxies will be emboldened and see their use of terrorism and regional military interference vindicated if Tehran is able to secure a permanent military and intelligence base in Syria and if it is able to take credit — deservedly or not — for a U.S. withdrawal from Syria.

Pulling out of the Iran nuclear deal and sanctioning Tehran will amount to little if through other actions the president undermines his own Iran strategy. Indeed, one of the 12 demands Secretary of State Mike Pompeo made of Iran was that “Iran must withdraw all forces under Iranian command throughout the entirety of Syria.” If the United States is not willing to do what is necessary to see that demand fulfilled, why would anyone else?

A U.S. withdrawal from Syria would mean leaving Israel to counter Iranian support for Hizballah on its own , increasing the dangerous possibility of direct conflict between Israel and Iran. In May, Iran fired rockets at Israel from bases in Syria only a few months after launching a drone from a Syrian base into Israeli airspace. It would also increase the likelihood of conflict between Israel and Hizballah, as underscored recently by the exposure of Hizballah’s precision rocket and attack tunnel programs.

The administration has been aggressively pushing for action in response to Iran’s assassination plots in Europe, provision of weapons to proxies in places like Afghanistan, Bahrain, Lebanon, the Palestinian territories, Yemen, and threats to disrupt freedom of maritime navigation. At a time when Washington is pressing allies in Europe and elsewhere “to stand up to Iran-backed terrorism,” suddenly abandoning a mission it described just a day earlier as a critical part of its strategy to counter Iranian malign activities undermines the Trump administration’s credibility regarding Iran.

Both Iran and Hizballah believe they successfully pushed U.S. forces out of Lebanon in the 1980s as a result of the U.S. embassy and Marine barracks bombings in Beirut, and have persistently drawn on that lesson in the years since. In 1988, for example, the CIA assessed that Iran sees sabotage and terrorism as effective tools in part because it assessed that the U.S. withdrawal from Lebanon humiliated the United States and effectively questioned the idea “that Washington could use its military forces to influence political developments in the Middle East.” Sanctions alone will not deter Iran, especially when Tehran sees Washington backing down from the use of more muscular undertakings such as maintaining a military presence in Syria.

A response to Iranian-sponsored terrorism is necessary, however, as the CIA noted in 1985 after a spate of Iranian plots: “If the U.S. fails to respond to attacks by Iranian-sponsored groups, Iranian terrorism will continue and likely grow.” Today, perceived battlefield success in Syria has brought Iran’s Islamic Revolutionary Guard Corp significant prestige , and Iran would see a U.S. withdrawal as a victory of its own making. Moreover, in contrast to the United States, Iran’s allies see the Guard Corps as a reliable ally that stays the course. Contesting Iran in the Middle Euphrates River Valley presented an opportunity to deny Iran key regional objectives at only modest cost.

Not Too Late

It is not too late to save the Washington’s Syria policy, and by extension its counterterrorism and Iran strategies. The U.S. military deployment to Syria is small, inexpensive, and exceptionally effective, but in the event the decision still comes down to a drawdown of U.S. forces in Syria, it should include concrete plans to mitigate the potential benefits for the Assad regime, ISIL and al-Qaeda, and for Hizballah and Iran. Such plans could include a phased withdrawal in northeast Syria, a commitment to remain at the Tanf base near the Jordanian border, increased assistance to local partners like the Syrian Democratic Forces, negotiating an agreement with Turkey to continue to fight ISIL and support the international anti-ISIL coalition, an explicit commitment to keep U.S. forces in Iraq and especially along the Syria-Iraq border, and a commitment to continue the U.S.-led air campaign in Syria.

Good policies are not made by tweet on a whim in a phone call with a foreign leader, but are the product of a robust interagency process in which facts and data feed into an informed and considered National Security Councio policy making process. The president clearly wants to revisit America’s Syria policy, which is his prerogative. He should ask his national security advisor to tee that up for debate and discussion, and then make an informed decision.

Matthew Levitt is the Fromer-Wexler fellow and directs the Reinhard program on counterterrorism and intelligence at The Washington Institute for Near East Policy. Aaron Y. Zelin is the Richard Borrow Fellow in the Washington Institute’s Reinhard program.

U.S. Army photo by Sgt. Nicole Paese