Speaking Wednesday night to PBS NewsHour, President Obama said the United States has definitively “concluded” the Assad regime used chemical weapons and backed what he called a “tailored, limited” response. Obama said a response is needed not just to prevent future attacks on Syrian civilians, but also to protect U.S. national security.

President Obama: “When you start talking about chemical weapons, in a country that has the largest stockpile of chemical weapons in the world, where, over time, their control over chemical weapons may erode, where they’re allied to known terrorist organizations that in the past have targeted the United States, then there is a prospect, a possibility, in which chemical weapons, that can have devastating effects, could be directed at us. And we want to make sure that that does not happen.”