I think people like Assad think differently - not sure if we can safely assume he thinks like we do. He might not care about political headaches - he’s a bully, a totalitarian dictator who’s killed many of his own people. Violence is the language he speaks and understands.
By Middle Eastern standards, Assad is a saint. Even the Syrian people have now rallied around him, sick of foreign powers tearing their country apart. And Russia has him on a tight leash. There’s no way he could use chemical weapons without Russian approval.
Neither Assad or Russia have anything to gain from it. They’ve already defeated ISIS. The American public have no interest in Syria. Only ISIS and their Israeli and Syrian puppet masters have any interest in prolonging conflict in Syria. They are the only plausible culprits of this alleged chemical attack.