Here’s another red vs. blue map, but this one shows the changes in partisan strength over the past quarter-century. (See larger version below.)
It’s from David Jarman at the Daily Kos. That’s a Democratic site (as is ThinkProgress, which flagged the map today), but the map is based on the most objective data possible — election results, as opposed to polls, skewed or otherwise. And it shows where the Republicans have made gains that have offset big Democratic gains in urban areas.
Jarman has a lot of fascinating county-level data (as does Ruy Teixera at ThinkProgress). His conclusion: “[Though] Democratic fortunes in the nation’s urban areas makes it easier to win the presidency, the corresponding decline in the rural areas makes it harder to win the House (without which, of course, you don’t accomplish much).”
Comparing the election map to a county-level map of religious affiliation, as published in the Washington Post (see below), it’s apparent that the biggest Republican gains have been in largely Protestant (shown red, green, and gold) and Mormon (gray) counties.
One exception is western Pennsylvania, which has been part of the Greater Appalachian shift to the Republicans despite its Catholic plurality (shown in blue). The Republicans have been fixated on Pennsylvania during the past few elections, and if they can somehow expand on their success there, they’ll have a much better shot at an Electoral College majority. But the Pittsburgh area is notable for its high percentage of white non-Hispanics and low number of immigrants (which means little or no population growth), so lessons learned there may not apply to many other areas.