Trends in my above chart:
Indiana:
The Hoosier State has been Pretty solidly Republican for the entire duration of the chart. It only went Democratic in the Democratic landslide victories of 1964 and 2008 and even in those it was still much more Republican than the nation as a whole. It appears to be perhaps trending somewhat more Republican with the exception of 2008 which looks like an outlier.
Iowa:
The Hawkeye State is the toughest one to get a read on. It is the only of these nine states that has been both the most strongly Republican (1960) and the most strongly Democratic (1988). Amusingly, when Iowa was the furthest of these nine to one side, both time that side lost. I honestly have no idea why Iowa was so strongly Republican in 1960 and 1968 nor why it was so strongly Democratic in 1972, 1984, and 1988. Other than those five and 2016, Iowa has been very close to the National vote.
Ohio:
The Buckeye State bounced back-and-forth between being slightly Democratic and slightly Republican from 1960-1972 then settled in slightly more Republican for nine of ten elections from 1976-2012 (and only VERY slightly more Democratic in the lone exception of 2004) then took a sharp right turn in 2016. There does appear to be a slight righward trend that predates 2016 but it is VERY slight.
Wisconsin:
The Badger State was Republican in 1960, 1968, and 1976 but Democratic in 1964, far left in 1972, and pretty strongly Democratic in the three elections in the 80's. There was a sudden rightward shift between 1988 (5.76% more Democratic than the Nation) and 1992 (0.66% more Republican than the Nation) and I don't know why. What is interesting is that the 88-92 shift appears to have been more-or-less permanent as Wisconsin has been slightly left or slightly right ever since.
Pennsylvania:
The Keystone State was, rather notably, part of Trump's winning coalition in the last election but their rightward drift started long before the 2016 election. As recently as 1988 Pennsylvania was to the left of California and about even with Illinois at around 3% left of the nation as a whole. Since then, Pennsylvania has become more competitive. In the seven elections since 1988 Pennsylvania has averaged just 1.10% left of the nation and never been more than 2.5% left of the nation. That said, Pennsylvania voted left of the Nation in every election from 1960-2012 but moved sharply right in 2016.
Michigan:
In 1960 and 1964 Michigan was the furthest left of the nine states shown here. Even in 1968 and 1972 Michigan was still one of the furthest left. The 1976 election is a bit of an outlier due to Michigan native (and former Wolverine Football Player) Gerald Ford heading the Republican ticket. Maybe it was a carry-over from voting for Ford or maybe those "Reagan Democrats" that you may have heard of were a real thing, at least in Michigan because Republican Presidential candidates did pretty well in Michigan in 1980, 1984, and 1988 but then Michigan drifted back toward where it had been in the 60's peaking with Obama doing 4.68% better in Michigan than he did nationally in 2008. The last two elections saw Michigan make a sharp rightward turn moving to just 3% more Democratic than the Nation in 2012 and a little over 1% more Republican in 2016.
Minnesota:
This one has the most clear long-running rightward drift. From 1968-1988 (six elections) Minnesota was either the most Democratic of these nine states or the second most Democratic and the state was at least 5.49% more Democratic than the nation in each of those six elections. In the 90's the state was about 4-5% more Democratic than the Nation and since then it has been a competitive state. In the five elections from 2000-2016 the State has averaged just 1.45% more Democratic than the Nation and only once (3.01% in 2004) was it more than 2% more Democratic than the Nation. In 2016 the State voted slightly more Republican than the Nation which had not happened previously within the bounds of this analysis.
Illinois:
Illinois has gone from being a battleground state in the 60's, 70's and 80's to being solidly Democratic today. In the eight elections from 1960-1988 Illinois averaged just 0.49% more Democratic than the Nation with a range from 2.89% more Democratic in 1988 to 2.07% more Republican in 1976. In the seven elections since 1988 Illinois has averaged 6.56% more Democratic than the Nation and never been less than 4.86% more Democratic (1996).
California:
In the eight Presidential elections from 1960-1988 California averaged 0.26% more Republican than the Nation. However, that is probably a big skewed by the fact that Californians headed the Republican ticket in five of those eight elections (Nixon in 1960, 1968, and 1972; Reagan in 1980 and 1984). California's leftward drift started long before it became apparent. Californians Nixon (in 1972) and Reagan (in 1984) actually did WORSE in their home state than they did nationally and in the last five elections Republicans have done increasingly worse in California than they have done Nationally each time out.
I don't know that there is an overall trend in the upper midwest but there was a massive rightward shift in 2016. Note that in 2016 the Republican candidate did much better than their 2012 predecessor in Indiana, Iowa, Ohio, Wisconsin, Pennsylvania, Michigan, and Minnesota while doing worse in Illinois and California. That sentence pretty much tells you everything you need to know about the 2016 election: Trump did better than his Republican predecessors in competitive states where it mattered and worse in non-competitive states where it didn't matter.
The big question going forward is whether the massive Republican improvement in those competitive great lakes states in 2016 is a sustainable structural change (like the rightward shift in WI in 1988-1992) or a one-time blip (like the rightward shift in Iowa in 1964-1968). If it is only a one-time blip then Republican's are in serious trouble because with Virginia turning blue (or at least purple) and some other formerly solidly red states turning purple the Republicans can't compete unless one of two things happens:
- There is an unexpected major rightward shift in some other currently democratic area, or
- Republicans can keep at least most of the great lakes states in reach.
