Agree with both USA4ME and Doc. The Russians have a much higher tolerance for casualties in ground ops than we do, a fact lost on the most of the people currently in a position to make decisions about it, both military and civilian. They didn't leave Afghanistan just because of casualties, but because it wasn't going anywhere for them and a shift in Russian political winds (Yeah, Russian, because Soviet politics were entirely about Russia, not the rest of the SSRs). The various Oministration flacks snarking about Putin being drawn to his destruction in asymmetric warfare in Syria are quite mistaken, there are clear things for the Russians to gain in Syria and they will pursue them to the limit of their very-considerable abilities once they decide to go in. The Russians are also not constrained by Western ideals of pinpoint surgical attacks with an absolute minimum of collateral damage, they do it old school, and old school works pretty damn' well.
An interesting stat I encountered the other day, in light of all the bilgewater on cable about WW2: 7 out of 8 deaths in WW2 were Russians and Germans. The Russians have a whole different frame of reference than we do in these decisions, when they think their national strategic interests are at stake.