At this point the details of what exactly happened outside Damascus this morning are still emerging. The preliminary evidence—based on amateur videos, photographs, and eyewitness testimony—indicates a large-scale attack using an unverified nerve agent that is likely not sarin. Unconfirmed reports indicate hundreds of civilian deaths in circumstances consistent with a chemical attack. The Obama administration has previously stated its belief that elements of the Assad regime have used chemical weapons on a small scale, but today’s attack—if verified—would represent a serious escalation in the use of these weapons. President Obama has also stated that, “a red line for us is [if] we start seeing a whole bunch of chemical weapons moving around or being utilized. That would change my calculus.”
The obvious question now surrounds how the United States and the international community should respond to deter the further use of these weapons, thereby preserving long-standing international consensus against the use of chemical weapons, without worsening the humanitarian situation in Syria and the wider region. For the United States, there is now also a vested interest in maintaining President Obama’s credibility in light of his publicly stated red line.This article was originally published in Bulletin of the Atomic Scientists.