The overthrow of Syrian President Bashar al-Assad after 13 years of civil war happened more quickly and with far less bloodshed than anyone expected. It was especially surprising that the Assad regime ended with a whimper and not a cloud of poison gas. During the course of Syria’s brutal civil war, Assad used chemical weapons more than 300 times against his own citizens, causing thousands of casualties. The worst such attack was a barrage of sarin-filled rockets launched against the Damascus suburb of Ghouta in August 2013 that killed an estimated 1,400 people. Haunting pictures of rows of small bodies covered in white sheets—some of the 400 children who were poisoned in the attack—became emblematic of the Assad regime’s cruelty. Thankfully, a similar scene did not repeat itself as rebel groups advanced on Damascus as part of their lightning offensive.

Although Assad is gone, the specter of chemical weapons still hangs over Syria. Before 2013, Western intelligence services estimated that Syria had one of the largest chemical arsenals in the world, including sulfur mustard, VX, and sarin. Although Syria destroyed its declared stockpile under international supervision following the Ghouta attack, it failed to account for tons of nerve agent precursors, hundreds of tons of sulfur mustard, and thousands of chemical munitions that it had produced before 2013. In addition, there are worrying signs that the regime had sought to reconstitute its chemical weapons program by importing nerve agent precursors and rebuilding production facilities. Whatever chemical weapons Assad held on to after 2013, or had produced since then, are now unguarded and could be seized by the new government or stolen by insurgents or terrorist groups.

The United States must prioritize working with the new Syrian government, international organizations, civil society groups, and its allies in the region to ensure that Syria’s remaining chemical weapons are disposed of safely and securely, and to see that all Syrian officials who assisted the regime in carrying out chemical attacks are held accountable for their crimes.

COMPOUNDING RISKS

For the past 11 years, international organizations have been trying to eliminate Syria’s chemical weapons. In 2013, following the Ghouta attack, the Assad regime signed the Chemical Weapons Convention that bans these weapons. Under the supervision of the Organization for the Prohibition of Chemical Weapons, the international organization charged with implementing this treaty, the regime destroyed its declared chemical weapons stockpile, which included 1,300 tons of chemical weapons and ingredients. But even while the regime was destroying its declared weapons, the Syrian military started using a new type of chemical weapon, chlorine barrel bombs, as part of its brutal counterinsurgency campaign against the opposition.

Moreover, Damascus’s cooperation with the Organization for the Prohibition of Chemical Weapons was limited. The regime denied the OPCW access to some of its personnel, delayed the process of destroying precursors, and refused to disclose the true extent of its chemical weapons research, production, and testing. Damascus never accounted for the fate of 360 metric tons of sulfur mustard (enough to fill thousands of artillery shells) that it claims to have destroyed at the outset of the civil war. Suspicions that Syria had retained undeclared chemical weapons were confirmed in April 2017, when the air force launched a sarin attack on Khan Shaykhun, a rebel-held town in the country’s northwest, killing nearly 100 civilians, including 33 children.

The Assad regime, with assistance from Moscow, also launched a massive propaganda campaign against OPCW investigators and local evidence collectors. According to survivors of the chemical attacks, the security services coerced civilians, many of whom had lost children in the attacks, to repeat the lie that it was the rebels who had used poison gas against their own communities.

The OPCW’s dogged investigation of Syria’s chemical weapons program had forced the regime to modify its declaration 20 times and admit to previously concealed research and production facilities. According to the organization’s latest report, published in late November, “Large quantities of chemical warfare agents and munitions” remain unaccounted for. At the meeting of the OPCW executive council last week, Director-General Ambassador Fernando Arias expressed concern that Syria may now have chemical weapons that “include not only residual elements but also potential new components of a chemical weapons program.”

If the fall of Assad triggers a new phase in the conflict, the former regime’s chemical weapons may become a prize sought after by competing rebel groups. So far, three of them—the former al Qaeda affiliate Hayat Tahrir al-Sham (HTS), which led the revolt, and two militias in southern Syria—have issued statements pledging their support for international efforts to eliminate the country’s remaining chemical weapons. HTS’s leader and the new de facto ruler in Damascus, Ahmed al-Sharaa, who renounced ties to al Qaeda in 2016, should capitalize on this commitment and work with the OPCW to resolve outstanding issues and destroy any remaining weapons or production facilities.

But even if the new leadership in Damascus wishes to eliminate Syria’s remaining chemical weapons, other actors in the country may not. The terrorist organization known as the Islamic State (or ISIS), which used crude and improvised chemical weapons in Iraq and Syria from 2014 until it was ousted from Mosul in 2017, is still active in the country. There is also a risk that Assad loyalists or extremist elements of the Alawite minority sect to which the Assad family belonged will start an insurgency. Such factions could potentially gain access to the chemical weapons concealed by the former regime. The longer it takes a new Syrian government to consolidate power and stabilize the country, the greater the risk that chemical weapons may be looted.

There is also a risk that Syrian chemical weapons experts may be recruited by terrorist groups or other countries. Over the course of its 40 year-long chemical weapons program, Syria mastered the production of deadly nerve agents and developed an arsenal of chemical munitions. The regime’s chemical weapons program employed an estimated 300 scientists and engineers—many of whom are now looking for new jobs. Iran and North Korea both possess chemical weapons programs that could benefit from their knowledge. Terrorist groups in Syria or in other regions may also seek to recruit these chemists-turned-mercenaries to develop new means of causing mass casualties.

INCENTIVES TO COOPERATE

In the face of these risks, military action alone—such as the hundreds of airstrikes that Israel has been conducting on Syria’s military infrastructure since the collapse of the Assad regime—is not a sufficient response. Such attacks can miss their targets, cause incomplete destruction, and destroy documents necessary to track down hidden weapons. Visits by international weapons inspectors are necessary to verify the fate of these weapons, ensure that they have not been stolen, and supervise their destruction. Israel’s destruction of the country’s military infrastructure, including the naval fleet and traditional weapons depots, also severely weakens the new state and reduces its ability to secure the country from internal and external threats. This could make governing authorities less keen to relinquish any military assets, including chemical weapons. Even Israel’s targeting of known chemical weapons facilities in Damascus may not be helpful, as the regime had likely moved its stockpiles to sites not known to the OPCW.

The United States, the European Union, and their partners in the region need to take several actions to address the proliferation threat posed by the chemical weapons that remain in Syria. First, they should make clear that their economic and political support hinges on the new government’s readiness to comply with the OPCW, which has requested that the Syrian leadership declare all remaining chemical weapons and production facilities and allow inspectors to verify their destruction. Al-Sharaa has agreed publicly to cooperate with the OPCW, but there is a risk that he will reconsider. He may have in mind the fate of Libyan leader Muammar al-Qaddafi, who had access to chemical weapons but failed to use them. In 2011, Qaddafi was dragged through the streets and killed by rebels after a NATO-led military campaign. In contrast, Assad first used chemical weapons in 2012 and held on to power for another 12 years before leaving the country comfortably on a plane to Moscow. The United States and its partners must dissuade the new Syrian government from holding on to the former regime’s chemical weapons as an insurance policy or to compensate for its depleted military capabilities.

Completing the verification and destruction of Syria’s chemical weapons program will be a major undertaking. The OPCW will need more resources—such as increased funding, additional inspectors, extra protective gear, and specialized equipment necessary for the inspection and destruction of chemical stockpiles—to ensure the rapid and secure elimination of Syria’s remaining chemical weapons. The cooperation of the new Syrian government and a stable security environment will be key to the success of such a mission. After the Libyan revolution in 2011, the new government in Tripoli informed the OPCW about the presence of undeclared chemical weapons that Qaddafi had concealed from inspectors. In a similar manner, countries with information on Syria’s chemical weapons activities, such as Israel and the United States, should share that information with the OPCW immediately. In the event that chemical weapons go missing or are looted in the post-Assad chaos, interested nations could fund a reward program to recover missing chemical weapon materials.

Finally, the fall of the Assad regime opens several potential avenues to hold accountable the former government officials, military officers, and scientists responsible for using chemical weapons. Although Assad and his family will remain safe from prosecution as long as they enjoy asylum in Russia, most other Syrians responsible for conducting chemical atrocities are not so lucky. The new Syrian government, civil society groups, and international partners should prioritize the collection of newly available government documents that can provide evidence of the regime’s crimes—and Syrian officials responsible for planning and conducting chemical attacks must be detained and tried. These steps are necessary for the Syrian leadership to craft a new comprehensive declaration for the OPCW, reduce the threat of proliferation, and begin a longer-term process to seek justice for the victims of Assad’s chemical atrocities. If the new Syrian government commits to these goals, it will need support—in the form of evidence, expertise, and resources—from foreign allies, domestic civil society, and international organizations. The United States has a strong interest in ensuring that Syrian war criminals are caught and convicted, which would send a message to others that there will be no impunity for the use of chemical weapons.

Although the Biden administration can start the process of destroying Syria’s remaining chemical weapons and supporting efforts to hold the perpetrators of chemical attacks accountable for their crimes, it will be up to the incoming Trump administration to see these actions through. During his first term, President Donald Trump demonstrated a strong commitment to enforcing the global norm against chemical weapons; in 2017 and 2018 he ordered two missile strikes to punish Damascus for using chemical weapons, degrading its ability to use these weapons and deterring it from conducting future attacks. In addition, the Trump administration imposed tough sanctions on the Assad regime for its human rights abuses and issued sanctions against 271 employees of the Scientific Studies and Research Center, which was responsible for Syria’s chemical weapons program.

In his second term, Trump has the opportunity to cement his legacy as the leader who ended the scourge of Syria’s chemical weapons. The United States and its partners in the region, working together with the OPCW and the new government in Damascus, can finally eliminate the threat of Syria’s stockpiles and strengthen the norm against these barbaric weapons.