Beginning with the Johnson/Goldwater blowout of 1964. From the 60s through the 80s there were huge shifts back and forth, whereas since 2000, and maybe arguably since 1992, certain patterns have fallen into place.
Modern politics have become known as the “post-ideological” era, but these maps may indicate the opposite. They point to a solidification of ideology along cultural divides which correlate with geographical patterns. Some years ago someone noted that the election results, particularly of 2000 and 2004, correlate to the free state/slavery breakdown prior to the Civil War. But demographics and cultural divides have shifted enough since then to conclude coincidence. Some of the reddest states used to be bastions of union and socialist activity. And California used to be almost a sure win for Republicans – the decline of military industry and ascent of high tech industry along with the growth of non-white voting blocs having reversed that pattern for the foreseeable future.
I think the map will look much the same in November, with the possible additions of Georgia and Arizona to the blue side, and curiously it’s conceivable that Iowa will go for Trump – for some reason he’s doing better in polling there than in Ohio, Florida, Virginia, and North Carolina.