Christianity in America

With the Republican Party relying heavily on America's Evangelical Protestant Christians for support as shown here:

...recent research by Pew would suggest that American politics is headed for a sea change. 

First, let's look at Pew's research which shows dropping regular (i.e. once a month or more) church attendance:

Over that past decade, the percentage of American who say that they attended church more than once monthly has dropped by 7 percentage points to 45 percent while the percentage of Americans who stated that they attended church less than once monthly if at all has also risen by 7 percentage points to 54 percent.  In the early 1970s, only 11 percent of American adults stated that they never attended religious services; by the late 2010s, this had risen to 27 percent, an increase of 16 percentage points or 145 percent.

Here is a graphic showing how the share of Protestants and Catholics have been shrinking and the percentage of "nothing" (i.e. no religious affiliation) has risen:

As well, over the past decade, there has been a broad-based decline in the share of Americans who identify as Christians and a corresponding rise in Americans who identify as unaffiliated, particularly among Generation X (born 1965 to 1980) and Millennials (born 1981 to 1996):

Not surprisingly, there is a very significant generation gap in American religious identity:

Data shows that there were 233 million adults in the United States in 2009 of which 77 percent identified as Christian resulting in approximately 178 million American Christians.  Today, there are roughly 256 million adults in the United States with only 65 percent identifying as Christian resulting in approximately 167 million American Christians, down 12 million over the decade.

One thing that will have an impact on future voting patterns is the share of white American Protestants who describe themselves as "born-again or evangelical" Christians as shown on this graphic:

Some of the drop of the number of white Protestant born-again or evangelical Christians from 19 percent to 16 percent over the decade can be attributed to the declining share of whites in the overall population and the dropping share of adults that describe themselves as Christians.

There is no doubt that the political landscape in the United States which is strongly influenced by the religious identity of voters is undergoing a massive change, a change that will have a significant impact on the voters that the Republicans have counted on for decades.  Religion also goes a long way to explaining the growing political divide in America as the left leans away from formal religion and the right clings to its belief system.