While Bashar al-Assad deserves to die a slow and horrible death at the hands of his victims for his wholesale slaughter of hundreds of thousands of citizens of his dictatorship, it is not up to the U. S. to do this. What the U. S. needs to do, is get the f#$% out of the region altogether, ASAP. Just leave. Just quit throwing good lives after wasted lives. Get out of Iraq, and Afghanistan. And, especially, quit giving money and selling arms to all the parties - especially Israel and Saudi Arabia, which are the REAL troublemakers in the region. They make Iran look absolutely reasonable by comparison. After all, we never overthrew Israel's or Saudi Arabia's democratic governments, like we did Iran's, now, did we? We also need to close the VAST majority of our 700+ military bases around the World (we especially need to quit torturing the good people of Okinawa with our presence), and cut our "defense" budget at least in-half, if not more.
I think that is why Bernie Sanders stumbles on questions about defense and our role in the Mid-East. Deep down he probably agrees with most of my assessment, but politically he can't begin to say a small part of what I am free to spout.