Although I’ve retracted the comparisons, Stewart is a very active speaker for the Progressive Democrats of America. Whether their venues are “major” or whether they are indeed “true Democrats”, I can’t say. But frankly, if it is fair to disassociate Democrats from everything left of a certain point, then it ought to be the same sort of deal for Republicans with respect to the right.
As it generally is, as people usually don’t come into the pit, quote remarks from members of the KKK (who, let’s face it, are more likely to vote R than D), and use them to pit Republicans in general.