There's no such thing. Honestly.
Obviously, anyone who thinks there are "Leftwing Extremists" has no idea what the Left wing supporters stand for at all. I may be wrong, but usually the word "extremist" has a connotation of violence, and Left wing supporters do not believe in violence in any sense of the word. So it doesn't really fit. Sorry.
"Dubya" has made America, what, $30 billion in debt now? I'm glad he cares so much about oil in Iraq, but really, doesn't anyone think that the hurricane crisis we are having here in America deserves some attention as well? It must be fun to be a Right wing supporter right now - especially one of those who think that Leftwing extremists exist.