I came across an interesting LA Times article:
Organized religion’s increasing identification with conservative politics is a turnoff to more and more young adults. Evangelical Protestantism has been hit hard by this development.
During the 1980s, the public face of American religion turned sharply right. Political allegiances and religious observance became more closely aligned, and both religion and politics became more polarized. Abortion and homosexuality became more prominent issues on the national political agenda, and activists such as Jerry Falwell and Ralph Reed began looking to expand religious activism into electoral politics. Church attendance gradually became the primary dividing line between Republicans and Democrats in national elections.
You can read it here