In 2013, Obama’s red line in Syria following the regime’s use of chemical weapons failed to produce any real intervention. Tuesday’s chemical weapon attack in Idlib, shadowing the Brussels conference where seventy countries gathered on the same day to determine Syria’s future, could be the Trump administration’s golden entry into the Syrian peace process. But, will he support the right side?

On August 21, 2012, Barack Obama warned Syrian president Bashar al-Assad that the movement or use of chemical weapons would cross the administration’s “red line” and trigger a U.S. military response. One year later, on August 21, 2013, rockets containing sarin gas pounded into the Ghouta suburb of Damascus, Syria. In the hours that followed, pictures and videos of the aftermath spread across the globe revealing the depth of the atrocities committed. By the time the sun rose that morning, as many as 1,500 civilians were dead. The Assad Regime had crossed the red line.

Obama’s “Syria Speech” delivered on September 10, a month after the attacks, declared to the American people plainly, first, that the Assad regime had violated international law and, second, that the United States and the international community must act against the use of chemical weapons for the protection of national and regional security, and civilians. His proposed response? Diplomacy over military intervention. Through the United Nations Security Council, Obama successfully pressured the Assad regime into admitting its use of chemical weapons and implemented a multinational plan (in conjunction with Russia) for destroying the regime’s remaining chemical weapons stockpile. He failed.

Early Tuesday morning, barrel bombs dropped from Syrian warplanes containing toxic chemicals slammed into areas of rebel-held territory in Idlib, Syria. Reuters reported as many as fifty-eight people were killed, including eleven children, and three hundred were wounded in one of the worst attacks since Ghouta in 2013. Chemical weapons usage has increased since Assad crossed the “red line” in 2013 with nine reported attacks in 2014 and 2015. UN investigators appointed by the Security Council confirmed the Assad regime’s responsibility for two chlorine attacks. It is likely the Assad regime is responsible for more. Two chlorine attacks occurring in August and September of 2016 indicate the Assad’s regime continues to violate the Chemical Weapons Convention, which Syria joined in 2013 as part of the Obama administration’s intervention. Beyond these reported attacks, Human Rights Watch has published further reports on the regime’s use of chemicals in aerial barrel bombs campaigns in 2014, 2015 and 2016.

Barack Obama’s “red line” stance and diplomatic intervention failed to prevent the use of chemical weapons in Syria. The continuity of the Assad regime’s deadly tactics reflects the need for a re-evaluation of U.S. foreign policy toward Syria. The Obama administration’s failure to impede Assad’s use of chemical weapons has resulted in two extreme consequences: the deaths of Syrian civilians and international skepticism of the United States’ effectiveness in the larger scope of the Middle East. This void has provided the Trump administration a critical moment to change the trajectory of U.S. policy both in Syria and in the region.

The Trump administration rode the wave of American frustration over Obama’s limited response in Syria into the White House. His hard stance on fighting the Islamic State and, more generally, terrorism remains his foreign policy priority in the Middle East. This past week, White House Press Secretary Sean Spicer and UN Ambassador Nikki Haley both echoed what could be a glimpse of the Trump administration’s policy moving forward in Syria, prioritizing the fight against terrorism and shifting away from discussions on Assad’s ousting. The shift in focus will likely be met with opposition from American allies. This shift comes at a critical point where the international community will demand some sort of response from the White House in response to alleged chemical attacks on Tuesday. The Assad regime’s chemical weapons use must be addressed. This attack provides ample opportunity for President Trump to reengage in the Syria peace process and take the lead in actively working through both diplomatic and military channels to stop the atrocities in Syria. This time, Trump must learn from the mistakes of his predecessor and apply the appropriate forms of power to pressure the regime to engage in the peace process and negotiate a settlement that ends the protracted conflict with a sustainable political solution. In the words of Joseph Nye Jr., “Smart power is neither hard nor soft. It is both.” It will take both to end the war, and Trump could be the one to accomplish it.

Jesse Marks is a Herbert Scoville Jr. Peace Fellow with the Protecting Civilians in Conflict program at the nonpartisan Stimson Center.

Image: Yarmouk Camp, Syria, in 2014. UNRWA photo