Do the election maps of 1964, 1968, 1984, 1996, and 2004 suggest a predictable trend in voting by party? http://www.uselectionatlas.org/RESULTS/
There has been a clear trend in presidential elections, but these particular elections are not all that good at showing it.
The 1964 and 1984 elections are particularly unhelpful for this. These were landslide elections in which regular trends were upset as popular incumbents (and/or very weak challengers) combined to make for very non-competitive elections.
Overall, though, the trend has been rather clear. The West Coast and the Northeast have become Democratic strongholds while the South and most of the interior of the country (with the exception of some states around the Great Lakes) are Republican. This trend has become stronger over the past few decades, though it was already starting to emerge in 1968.
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