I'd like to correct your thinking briefly...<quoted text>
We think this country has a 2 party system with a few independants sprinkled in..
We actually have factions withing the party's themselves.
The Democrats have the liberals, and the Republicans have the Neo Conservative's.
Liberalism is defined as open mindedness - a rather middle of the road approach.
You're thinking of leftists, not liberals. Leftism can be defined rather simply as anti-conservatism; for no rhyme or reason, just anti-conservative.(Though in fairness, conservatism could be defined simply as anti-progressive.)
Now to the point...
Leftists tend to vote Green, not Democrat. They hate Dems as much as they hate Republicans.
Though this is still oversimplified. In the Democratic party, and to the left of it, you will find progressives, socialists, communists, and all sorts of others. Some nutty, some rather reasonable... I favor the progressive wing myself.