He established the first Republican ticket without a Protestant since 1860, when Abraham Lincoln, who belonged to no church, chose Maine Sen. Hannibal Hamlin, a Unitarian as his running mate, says Mark Silk, professor of religion and public life at Trinity College in Hartford, Conn.

Yet today's GOP ticket — two Christians who are neither evangelical nor mainline Protestants — isn't a major marker of social change, University of California history professor David Hollinger says.

For a real sign of the decline of American mainline Protestantism, Hollinger looks to the Protestant-free U.S. Supreme Court: six Catholics and three Jews. The Romney-Ryan ticket is well in line with today's wider, less brand-specific Christian culture, he says.

The number of Americans who identify with a Protestant denomination has been steadily slipping from over 60% in the 1970s to 52% in 2010, says Duke University sociology professor Mark Chaves, who tracks religion statistics in the national General Social Survey, conducted biannually by the National Opinion Research Center.

With this comes a shift in assumption about values, says Stephen Prothero, author of The American Bible, examining core civic, political, literary and religious texts of U.S history and society. "We can no longer assume when people speak of American values, they're speaking in terms of Protestants who dominated American religious and public life" since the nation's founding, Prothero says.

Besides the Supreme Court's makeup, he cites today's diversity in Congress, which has Catholics, Mormons, Jews, Buddhists and Muslims.

The Bible isn't every candidate's go-to text any more. Prothero expects Vice President Biden, a Catholic, and Ryan to argue over their different views of Catholic social teachings rather than stand on Gospel quotations.

Some evangelicals claim Ryan as one of their own, says David Brody, chief political correspondent for the Christian Broadcasting Network and author of a book, The Teavangelicals.

Brody says that Ryan, as a "dedicated pro-life, true blue conservative," is a Tea Party evangelical, too, because he stands for the movement's agenda of "fiscal austerity and social conservatism."

Silk, who blogs at Spiritual Politics, points out, "I haven't heard any Protestants complaining that Romney didn't pick one of their own. The default mode is 'Christian' and Catholics are seen in the Christian tent."

Mormons see themselves as Christian and many scholars, but not all evangelicals, agree.

There's history to this. Joseph Smith, founder of the Church of Jesus Christ of Latter-day Saints in the early 1800s, "announced he had been called to set Christianity straight," says Robert Millet, professor of religion at Brigham Young University. Smith preached that the historic churches — their bishops, priests and pastors — had lost their divine authority and he offered a radically different vision of God, Jesus and the path to salvation.

Today, Millet says, "Mormons and Catholics are side by side with evangelicals in sharing very conservative beliefs in the traditional family, and in the idea that there are absolute truths and moral values."

The groups stand together in opposing abortion, same-sex marriage, and a provision in Obama's health care law. It requires employers, including faith-based institutions, to provide or facilitate employee insurance coverage for contraception. When the U.S. Conference of Catholic Bishops called the rule an affront to religious liberty, Mormons were right with them, Millet says.

The Bishop John Wester of the Catholic Diocese of Salt Lake City says "we have a healthy relationship and work closely on issues of compassion."

Ultimately, the symbolism of the Romney-Ryan ticket may be that it doesn't matter any more which religion a candidate claims as long as he claims one, says Grant Wacker, professor of Christian history at Duke Divinity School. "It would be much more significant if the candidates had no faith or called themselves agnostics or unbelievers. That is still unimaginable in the USA today," Wacker says.