Efforts to hold the regime of Syrian President Bashar al-Assad accountable for persistent chemical weapons use were dealt another major blow recently when the UN Security Council failed to pass a resolution punishing Syrian officials for their roles in chlorine attacks in 2014 and 2015. Absent UN action, the United States and its allies have only the findings of a joint Organization for the Prohibition of Chemical Weapons (OPCW)-UN investigation to sustain the drumbeat for punishing Syria.

Despite a concerted U.S. Government-led effort to establish an accountability mechanism in the UN, previous resolutions passed by the UN Security Council contained watered-down language meant to appease Syria-friendly countries like permanent Security Council members Russia and China. It was “no” votes by Russia and China that sank the latest resolution.

The Chemical Weapons Convention (CWC) would have to be bolstered if the Assad regime is to be rebuked for its use of chemical weapons. Leadership from the United States on this issue could send a message to allies that despite a change in government, the United States remains steadfast in its commitment to holding those who use chemical weapons accountable. For example, the United States could encourage its allies to levy sanctions against individual perpetrators the way the U.S. Government did in January. As the Trump administration continues to develop its Middle East policy, efforts to implicate Assad and his government for chemical weapons use should be part of their considerations.

Second, the United States and its allies could call upon the OPCW, which oversees implementation of the CWC, to be more vocal in condemning Syria’s actions. The OPCW’s special section on Syria has not issued a press release since Dec. 13, 2016. The organization responsible for implementing the CWC should be the leading voice of outrage in the international community regarding Syria’s continued chemical weapons use. Such statements could call attention to the recent veto votes in the UN Security Council by Russia and China. As signatories of the CWC, and allies of the Assad regime, the unwillingness of Russia and China to take a harder stance against Syrian chemical weapons use weakens their credibility as OPCW Executive Council members.

Syria has always been an outlier among the 192 States Parties of the CWC. As the only country to ratify the treaty after carrying out a devastating chemical weapons attack ­– in which 1,400 Damascus-area residents were killed by sarin in August 2013 – Syria agreed to the removal and destruction of its declared chemical weapons stockpile to avoid military intervention and acceded to the CWC that year.

While chlorine is not a banned substance under the CWC, the weaponization of any chemical by any party to the treaty is prohibited. The failure to bring Syrian leaders to justice for their continued use of chlorine as a chemical weapon speaks to a critical shortcoming in the international system responsible for enforcing treaties. The boldness with which Syria has flaunted its CWC obligations since allegations of its chlorine use first surfaced in April, 2014, is also unparalleled by States Parties. Syrian actions have arguably weakened norms against chemical weapons, which the Islamic State is also now using in Iraq and Syria. The OPCW-UN Joint Investigative Mechanism examined numerous allegations of chemical weapons use and returned proof of Syria’s culpability in many of these attacks. The same investigators also confirmed the Islamic State’s responsibility for a 2015 mustard gas attack in Syria.

The CWC is a critical component of the broader international order governing norms against WMD use. U.S. allies – without whom the 2013-2014 operation to remove and destroy Syria’s declared chemical weapons would not have been possible – are vitally important to upholding norms against chemical weapons use. With the path to UN Security Council action apparently blocked by Russia and China, the United States and its allies could seek to ensure the treaty’s continued relevance by bolstering its accountability mechanisms. That strength will only be credible if backed by concrete action that punishes Assad regime leaders for their flagrant violations of international law.

Natasha Lander is a senior policy analyst at the nonprofit, nonpartisan RAND Corporation.

Image: Oren Rozen via Wikimedia