[quote=@Vilageidiotx]
 He figures he has Russian protection and that the current US President is weak.
[/quote]

But he's pretty much on the cusp of victory, with or without chemical weapons. If the rebels were about to bust down his door to crucify him, I would understand how he might reach that level of desperation. But no, the dude's winning, has Russian support, and up until the gas attack had the indirect approval of the US because Trump seems to be okay with what is happening there with Russia. He is putting all of that in jeopardy, and for what? So he can taunt the US (and the world), hedging his bets on the belief that the US is still unwilling to enforce the red line? Seems way too risky and unnecessary. Then again, I'm not a crazy dictator, so who knows what's going on in his head.