A few months ago I made some graphs showing the movement of each state's PVI since the Civil War. I never got around to posting them as I was too busy to do a proper job of writing up explanations. Since I might never get around to a write-up at this point I'll just show the graphs as is.
The Y-axis measures "PVI" (Defined here as the difference between the two-party preferred Presidential vote in a state and the two-party preferred Presidential vote nationwide averaged over two elections) where a positive score is Republican and a negative score is Democratic.