The core divisions among religious Americans, and particularly Christians, are no longer defined by theological issues. The splits are political. The friendly (or at least usually friendly) arguments among believers over back fences and at kitchen tables or backyard barbeques tend not to focus on the Virgin Birth, the real presence of Jesus in the Eucharist, infant baptism, or the nature of the Trinity. More often, they are about issues such as abortion and gay marriage—and about attitudes toward government.
This has led to a peculiar kind of ecumenism. Historically, the defining religious divisions in our politics have been between Protestants and Catholics and between Christians and Jews. (Muslims have arrived to our shores in significant numbers only relatively recently.) In largely homogenous Protestant communities, there were also fierce feuds among denominations, particularly between Methodists and Baptists in smaller Southern towns. As in so many things in our history, racial divisions affected all groups. And many Protestant denominations split along regional lines around the issues of the Civil War. But on the whole, social and theological differences between denominations and faith traditions mattered a great deal.
Those old divisions have largely passed away. Now, conservative Catholics, Protestants, and Jews tend to ally together against liberal Catholics, Protestants, and Jews. As Grant Wacker, a professor of church history at Duke Divinity School, has said: "One of the most remarkable changes of the 20th century is the virtual evaporation of hostility between Protestants and Catholics. I don't think it's because Baptists have come to have a great respect for Tridentine theology. It's because they see Catholics as allies against graver problems. There's a large reconfiguration going on now." Wacker was speaking mostly of the conservative side of politics, but his words apply to moderates and liberals as well.