The Demise of the Republican Party?

According to Pew, only 28% of voters now call themselves Republicans. It seems sad to me that the enormous incompetence of the Republican Party over the past eight years seems to be leaving us temporarily with a one party system. While it seems clear that the Republicans deserve their fate, I worry about the absence of well-defined, opposed powers in the political process. I particularly worry because the further polarization of the remaining members can only make the Republicans even less relevant politically. A party that responds to the loss of so many members by moving further to an extreme can contain only the dregs of its former membership.