Political Party. Singular. And therein lies a problem - declines in theism are going to be unevenly distributed, and the political consequences of that variation may be amplified by variation in religious observance. The confusion of religion with theism will prevent clarity of observation as well as reason. Children of atheistic parents may be more likely to become religious than theistic, for example - especially in regards to an Abrahamic deity with whose believers they have long familiarity.