The steady movement of the Republican party towards total dominance by the crazies is undoubtedly going to hurt them in elections. Some argue that this is a good thing because it will make them marginalized. While this will undoubtedly make it easier for Democrats to win elections, especially at the Congressional and presidential level, it could well be a bad thing for progressive causes in general because of the general law that politics abhors a vacuum and that candidates will seek to fill as much space on the spectrum of viewpoints as they are allowed to get away with.
The more that the crazy base squeezes Republicans into a narrow space on the extreme right, the more likely it will be that the Democrats will change their message to make it appealing to those voters in the space that is being vacated. On the other hand, a sane and vibrant Republican party that advocates for traditional conservative programs will force the Democrats leftwards in order to be a viable alternative.
Republican candidates who are beyond the fringe enable any old Democrat, however awful, to look good by comparison. A case in point is the just concluded election for governor in Virginia. The winner was Democrat Terry McAuliffe, a sleazy, corrupt politician who should never have even won the nomination. But his opponent Ken Cuccinelli was a Tea Party extremist with terrible anti-women and anti-gay views and so what choice was there for any liberal or progressive? We saw how business interests aligned with centrist Republicans and the party establishment did not support Cuccinelli. They will now be courted by Democrats who will tailor their message to appeal to them.
On some social issues the Democratic party is still worth supporting. With McAuliffe at least there are some issues that I want to see advanced, like Medicaid expansion, that he will support. But we really should be able to do better than people like him. But if the Republicans go completely nuts, that is the kind of Democrat that we may increasingly see, who will be quite happy to shift their views on these issues rightward too since they will have little to lose by doing so.