It isn't a competition between US and Russia. Russia will drop a handful of outdated bombs (that aren't guided) in a last ditch effort to prop up Assad. US runs circles around that. The issue, in my mind, is that it is a threeway between Assad, al Qaeda and ISIS. Hard to know who to support in that scenario, other than the refugees caught in the middle. And by cold, realist calculus, with Iran and Russia throwing their more limited resources into the quagmire, strategically the best outcome is to keep letting them fight. A reckoning has been coming for this region for over a century. Strongmen as stabilizers was bound not to last.