Assad has probably murdered more people than ISIS. If he would stop barrel-bombing civilian neighborhoods and Russia would stop bombing aid convoys and hospitals, it would make it a lot easier to be their friends.
And USA arms and trains jihadist "rebels" (unless you are dumb enough to believe McCain's and Hillary's BS about the so-called "moderate opposition"). Today they are fighting Assad and tomorrow they will be blowing up buildings in NYC and Washington, like Al Qaeda rebels that USA armed and supported in Afghanistan in the 1980's. Talk about history repeating. You don't have to like Trump to concede his point that USA is being run by some really dumb people.
The Syrian civil war is nothing more than a new chapter is the eternal war between sunnis and shiites that has been going on since the 7th century (!) We have no business getting involved in that mess. Let them kill each other if they want, that's not our problem. ISIS is different because they are attacking western targets and have global ambitions. Destroy ISIS, with the Russians' help if necessary or convenient, and then get the hell out and let the locals sort things out between themselves.