attacking our other allies the Syrian Kurds, who did much of the hard fighting against the Islamic State around its old capital. We are paralyzed, caught in a web of our own making: we can't fight the Turks, because they are in NATO and we depend on our Turkish air base to keep our Middle Eastern wars going; we can't fight the Russians because we agreed to their setting in up Syria, and anyway we don't want a war with Russia, and on what basis could we complain about their helping our Turkish allies? We can't abandon the Kurds because they are our only really reliable friends in the whole godforsaken region, plus we would feel like cads for ditching them after working so closely with them for so long, not to mention the whole "losing face", "not following through on our commitments" thing that matters so much to so many American foreign policy types. And, we can't broker a peace deal in Syria because that would mean recognizing the Syrian government, which we have been saying for years is an illegitimate tyranny.
Near as I can tell, our Syrian policy is to keep muddling along until a democratic, human-rights-respecting, pro-America, pro-Israel, anti-Iran, anti-terrorist government miraculously appears in Damascus. Meanwhile, people continue to be blown up on a regular basis, and the whole region from Manchester to Amman is in crisis over what to do about refugees thrown up by this and other wars. There's no use blaming Trump's people for this, because Obama's had no idea what to do, either, and ended up focusing on the Islamic State because that was one problem we felt like we could solve. They seem to be pretty much beaten. But Syria's ordeal seems likely to stretch on for decades.
On the map above, territory controlled by the Syrian government is in red, Kurdish territory in yellow, other rebels in green, and the remnants of the Islamic State in gray.