So far, the American invasion have turned Iraq from a secular Qaeda-free dictatorship into an anarchy and haven for terrorists. It also boosted oil prices. You'll get another Iraq (and Vietnam in several years, yes, it was all right in Vietnam at first, too) in Syria. If Russia fails in her attempt to save the USA from another blunder in Middle East.
Already American resourses are stretched (remember Louisiana National Guard). A Russian proverb: where it's thin, it tears.
Some people here have mentioned Russian anti-Americanism. Its extents seems to be over-estimated. However, sending bombers all over earth doesn't help promote love to America. You start to think who's next.
I've read invectives above about unpleasant "Russian" communities in Brooklyn and Brighton Beach. It's funny; people don't realise that they are not only being politically incorrect and racist, but much, much worse -- anti-Semitic. For those ghettos are populated by Jews, not Russians.