Jeffrey Rudolph has an interesting article that sheds some light on this religious segment and walks us through the various groupings that make them up and their relative strengths and goals.
He says that twenty-six percent of the US population is affiliated with the Evangelical Protestant tradition but adds:
It is useful to distinguish between two broad groups of evangelicals: (i) moderate evangelicals who concede that there is more than one legitimate way to worship and serve Christ; (ii) traditional evangelicals—which include those identified as fundamentalists—who come closest to the “Christian Right” discussed in the media. Traditional evangelicals, approximately 12 percent of the U.S. population, are overwhelmingly Republican, openly hostile to democratic pluralism, and promote policies that deny the civil rights of others (such as gays and Muslims).
He also says that contrary to popular belief, it was not the 1973 Roe v Wade decision that galvanized the religious right into heightened political activity but the revocation by the IRS in 1976 of Bob Jones University’s tax-exempt status. The abortion issue was added later as an additional rallying cry.
Until that time, the religious right was indifferent to economic issues. But wealthy business interests realized that a strong anti-abortion stand might bring into the movement those who were not enthusiastic about tax cuts or business deregulation. This is what enabled wealthy Republican interests to attract members of the poor, working, and middle class to support them, even though it goes against their own economic interests.