The Rs and the Ds have lost much of their tails. The "unaffiliated" have most of the bell curve. The losses of the population of the "2 party system" means that the "unaffiliated party" grows and is now meaningful. The tails of the bell curve are now left with the most radical minds since the normal voters of both parties have decided to leave their R and D parties.

The tails are left with the radicals of both parties who believe they speak for (a diminishing) voting block. Normal people are leaving and want nothing to do with the remaining "crazies." of either party.

:-)