Well, it's come to be a non-so-subtle euphemism for someone under the control of our Zionist overlords. That's why the Marxist moonbats direct the word almost exclusively at Jews (and their "pawns") and say it as though they're spitting out poison.
I'm not sure why former Democrats who saw the light and became conservatives would need their own special sub-category... considering that many (if not most) of us were liberal Democrats when we were young.