Leverage in Syria for no benefit to us? Why do we need leverage in Syria, exactly?
People can call it a "win for Putin" all they want, but the reality is it's a win for the Syrian people. Over 500,000 refugees have returned to their homes in government controlled Aleppo and Damascus this year. The cities are being rebuilt, markets re-opening, even Christian churches (which are...you know, legal there. Unlike some other neighboring countries).
He may have done terrible things, but Assad has the support of the vast majority of Syrians. I'm also not convinced he intentionally gassed civilians this year, since it made absolutely no sense strategically and his army was already winning, but that's another matter entirely.
The US will continue to make deals with SA no matter who's in power, because Petrodollar. I give a lot of credit to Rand Paul for consistently voting against those deals, despite some of his other policy ideas.