If anything the Russians are proving that you can intervene and be successful if you actually have any sort of coherent strategy and the right allies on the ground. They are the ones bringing an end to this bloody affair (with a lot more blood but still).
EDIT: https://en.wikipedia.org/wiki/Timeline_of_the_Syrian_Civil_W...
So for 3.5 years the US tested the "let's stay out of it and see what happens" strategy (for the most part). What happend? 6 million people internally displaced, 5 million refugees outside Syria, 500,000 people dead. Iran, Russia, Hezbollah, Assad emerge as winners. Well, that really worked out. Not to say they wouldn't have messed it up by intervening but this bad? Hard to imagine.
EDIT2: I also understand as a non-american that it's a lot to ask of the US to take care of the world. But if it doesn't, who will? What happens in the rest of the world ends up impacting the entire world, including the US. Maybe I'm too naive though :(