Glenn Greenwald has responded via his regular Salon feature (8/6/09, ad-viewing required) to Rush Limbaugh, "speaking to his audience of 15 million, compar[ing] Barack Obama to Adolph Hitler and Nancy Pelosi to Nazi leaders," by asking you to instead
compare (a) the way that a single anonymous person's comparison of Bush and Hitler swamped our political discourse and forever altered the image of MoveOn with (b) what the (non)-reaction will be to the identical comparison coming from the leader of the Republican Party who spouts his hate-mongering to an audience of 15 million people. Within that comparison one finds many central truths about how our political debates and media discussions function.
Looking beyond how corporate media pilloried Democratic activist group MoveOn over user-submitted (and never-published) video, Greenwald gives a maddeningly extensive history of corporate media compliance with right-wingers' Nazi smears, and simultaneous reprobation of even spurious such instances from the left.
See the FAIR Action Alert: "When Are Nazi Comparisons Deplorable?: For Fox News, Only When Republicans Are the Target" (1/16/04).