A sudden and overwhelming shift of Christian conservatives from the GOP to the more secular-minded Democratic Party appears unlikely. As Laura Olson, an expert on religion and politics at South Carolina’s Clemson University, put it: “The Republican Party is still going to be, at a minimum, the lesser of two evils.”

But in politics, subtraction can be just as important as addition. If large numbers of evangelicals were to stay home on election day, or channel their activism into outlets other than politics, the GOP could suffer grave consequences; over the last generation, devout churchgoer voters have become an increasingly vital part of the shrinking Republican base…

Historically, evangelicals have cycled through periods of political engagement and withdrawal from the electoral scrum. The latest activism began in the 1970s, when liberalism had evidently run its course and religious leaders like the late Rev. Jerry Falwell galvanized Christian voters and turned them into a force for conservative values and political change.

“We may be coming to an end of [that] cycle,” said Corwin E. Smidt, a pollster and political scientist at Calvin College, a Christian liberal arts school in Grand Rapids, Mich. If nothing else, Smidt said, scandals like the Sanford affair make religious voters “more likely to second-guess themselves . . . and certainly increase disillusionment.”