The GOP was really rather good at dominating the political landscape when it was all about the advertising. In the 80s and 90s (and probably the 60s and 70s too) the only way you could get your message across was to be the person with the most money to bid on airtime. Now any little shit with a webcam can do it almost as effectively, and it's changing the message.
Which is not to say the Dems are an unstoppable force now. Playing against the interests of the people with money hurt them for sure, but the real problem is and has always been the ivory tower attitude. They are "above" doing the sort of base attention-getting described above, and that's going to come back and bite them in the ass again if they're not careful, because cheap tricks work just as well on the internet as anywhere else. Obama's like this too, but he manages to do well for himself by being exceptionally better than the opposition at what he does and taking full advantage of the fact that they haven't caught up with the changing landscape yet. But you can only shrug off so many low blows; eventually he and the rest of the party are going to have to learn to play the same game. Clinton could, and for the most part he could handle it; he fell off the slippery slope more often than anybody's comfortable with, but on the whole I think we're still better off for it.
