If the US intervenes militarily, it can.
If the US sends in troops, I'd be like if Russia sent in troops to protect the L.A. Rodney King rioters. How do you think the US would have reacted to THAT? It's not the best analogy, but that's how it would feel to the Russian government.
If the US intervened, I think the conflict would eventually escalate into a strategic nuclear exchange (WWIII) after many Russian and American soldiers die fighting each other. Russia still has 2,000+ nuclear weapons aimed at the US. They do not have the ability to project conventional power, so a strategic nuclear response will be one of their few options.
That would suck, bad. Start stockpiling penicillin, water and ammo, people!
All that being said, we are spread too thin right now to get involved. The Georgian president started this invasion without consulting us and probably expected our support, which he is not getting so far. We will stay out of it.