As a former conservative (and a former leftist; I got around), I have noticed that the mainstream media often use the term "ultra-conservative" but rarely apply any equivalent term to extremists on the Left. (I use Left/leftist because I mean to reclaim the term "liberal" for libertarians.) Evidently, there are no left-wing extremists, only right-wing extremists.
But maybe President Obama's press secretary Robert Gibbs gave the mainstream media a term they can use: "the professional left." Venting about these left-wing extremists in his own party, Gibbs said:
They will be satisfied when we have Canadian health care and we’ve eliminated the Pentagon.
President Obama has repeatedly stated his preference for a single-payer health care system, such as they have in Canada. Does that make him a semi-professional leftist?