I think the democrats being against troops leaving is threefold. One is leaving allies in the lurch, two is leaving the Kurds in harm way, and three leaving Israel in danger. I am not saying I agree, I don't really know enough about all the particulars to make an informed comment regarding the Kurds and Israel in connection with Syria.
All I know is that I agree we have too much of our military in the Middle East and we should withdrawal from all those areas, Iraq, Afghanistan and Syria. I don't see how staying in any of those areas with no end game in sight is a good policy. That goes more for Iraq and Afghanistan than Syria.
Unless we invest in the rebels of Syria and really invest a lot more than we currently have at this point to really make a difference and actually destroy Assad's government, I am not sure what the point is in our being there. ISIS is just another extremist group, we could probably better manage by intelligence work and special operations and smarter drones. IMO
What I am getting at, I think it is unfair to say the opposition to withdrawal of our troops from Syria is just a hate Trump thing. I don't agree with them, but there are genuine reasons for some democrats to feel the way they do.