Hello, Heterogeneity - NYTimes.com Between 1948, when American National Election Studies first surveyed the electorate, and 1970, the percentage of voters who were white didn't change much, ranging from 89 to 91 percent. ANES didn't begin breaking out data on mainline and evangelical Protestants until 1960. Traditional mainline Protestants - including Episcopalians, Presbyterians, Methodists and Lutherans - constituted a decisive plurality of the electorate at 45 percent. Evangelicals stood at 29 percent and Catholics at 20 percent. Only one percent defined their religion as "none." By 2008, whites had fallen to 74 percent of the electorate. The following chart, produced by Alan Abramowitz, a political scientist at Emory, shows the minority ("other non-white" and "black") share of the vote from 1992 (13 percent) to 2008 (26 percent), with an estimate for 2020 (34 percent). In a study published in February 2008, the Pew Forum on Religious and Public Life found that mainline Protestants, once the dominant force not only in politics but in the national culture, had fallen to 18.1 percent of the electorate, behind both Protestant evangelicals and Catholics - and barely ahead of the fast-growing category of "unaffiliated," which reached 16.1 percent. Although a majority of the American population today decisively self-identifies as Christian, at 78.4 percent, America and its politics have in fact become vastly more heterogeneous. The connection between religion and politics is very complicated, of course. On the one hand, many people do not feel their political beliefs and their religious beliefs are directly related, but for many others the former determines the latter. Not to mention the fact that the tenets of Christianity are themselves subject to partisan and subjective interpretation. Take a provocative query posed in an April 2011 survey by the Public Religion Research Institute: Is capitalism compatible with Christian values? By two to one, 53-26, Democrats believe that capitalism and Christianity are not compatible. Republicans, in contrast, believe there is no conflict, by a 46-37 margin. Tea Party supporters are even more adamant, believing that capitalism and Christian values are compatible by a 56-35 margin. These very different notions of what it means to hold Christian values correlate, in turn, with beliefs concerning core political issues of equality and social mobility. In September 2011, the Public Religion Research Institute asked respondents to choose between these two ideas: a) "one of the big problems of this country is that we don't give everyone an equal chance in life" b) "it's not really that big a problem if some people have more of a chance in life than others." The results again show sharp differences of opinion tied to partisan identification: Some issues are less confounding. For example, a January, 2012 P.R.R.I. poll question on same-sex marriage revealed a wide split between religiously observant and non-observant constituencies. These findings reflect - and drive - the growing polarization of American politics. But here's the surprising thing. Given the scope of the demographic and ideological transformation of the United States over the last six decades, it's interesting that the two-party system has not imploded. In the face of sustained centrifugal upheaval - including a proliferation of religious affiliations, the enfranchisement of substantial minority populations, rising levels of economic inequality, and the belief among a plurality of voters, 44 percent, that our economic system (capitalism) and the religious identification of three-quarters of the electorate (Christianity) are not compatible - we still are a nation of Republicans and Democrats. How will the center-right adapt when it becomes clear that its dependence on white voters threatens its ability to compete as a national party? As presently constituted, the Republican party has become the party of the married white Christian past. This stance proved effective in the 1970s and 1980s, and again in 1994 and 2010, but time is running out. Will the party, of necessity, become more amenable to religious diversity? Will conservatives embrace immigration reform? Will Republicans try to drive a wedge between Hispanic and black voters in an effort to fracture the Democratic coalition? Will Republicans look to a more subdued form of capitalist competition? How will the Democratic Party cope with the fast approaching moment when non-Hispanic whites become a minority of its voters? Will Democratic presidential nominating contests become explicitly racial and ethnic? Will religious non-observance and a larger role for the state in the economy become explicit hallmarks of the center-left? While a number of political and demographic analysts see current trends giving the Democratic Party an inevitable advantage in the near future, the history of two-party competition - and the continuing 50-50 split in American politics - suggests that the out party, sooner or later, responds to negative feedback and changes course. The only guarantee? Neither party's future is assured. Thomas B. Edsall, a professor of journalism at Columbia University, is the author of the book "The Age of Austerity: How Scarcity Will Remake American Politics," which was published earlier this year.