With a candidate as strange as Donald Trump, it is tempting to speculate that the usual red-state and blue-state assignments may not hold. Trump is probably not a leader of change in the Republican Party, but rather the visible manifestation of a realignment within the party that has been brewing for years. Will national voting patterns change too?
Probably not. State-by-state party preferences mostly change in a gradual manner. Today I will show that the last major national rearrangement happened in the years surrounding 1964 – when President Lyndon Johnson signed the Civil Rights Act.
It is not easy to tell simply by examining election results when a realignment has occurred. For example, from 1988 to 1992, Democrats went from winning 10 states (Dukakis) to 32 states (Clinton). However, that was principally driven by a nationwide shift in Democratic-Republican vote margins.
To detect when the electoral map has been rearranged, I will use the correlation coefficient, a measure is not affected by national swings in opinion. The maximum possible value for correlation coefficient is +1.0, which indicates perfect proportionality with only an offset. (A value of zero indicates no relationship, and a value of -1.0 indicates a perfect anticorrelation.) In this definition, an across-the-board shift is not a “realignment” but just a strong year for one party.
In this example the average difference was nearly 13 percentage points, which is not a real realignment. On top of that was a state-by-state standard deviation of 7 percentage points. That 7-point deviation measures the extent to which states are genuinely realigning.
This is pretty typical of consecutive Presidential elections. Here is a graph of election-to-election correlation coefficients since 1964:The biggest change here is the election of 1964, when national patterns of support for Johnson v. Goldwater were totally uncorrelated with patterns of support for Kennedy v. Nixon. The sharp change coincides with President Johnson’s signing in July 1964 of the Civil Rights Act. From 1960 to 1964, the average state Democratic-Republican margin moved 19 points toward Democrats…but the standard deviation of additional change was a whopping 25 percentage points. Now that’s a realignment!
A little more re-sorting of partisan voters took place over the next three elections, interrupted only by the election of 1976, in which Carter temporarily regained southern states for Democrats. In 1980, the major realignment became complete.
Since 1980, the pattern of partisanship has changed only a little bit from election to election. Note that the graph above includes current 2016 polls of the Clinton v. Trump race; the correlation with 2012 is +0.90. So far, no realignment is apparent.
Changes accumulate over time, as shown by this set of comparisons of different years with the 2012 election:Again, the overall pattern is a sudden change from 1960 to 1964, and gradual change occurring since then. In this graph, you can see the transient effect of southerner Jimmy Carter quite well as a notch in the graph for 1976 and 1980.
Incidentally, correlations are useful for comparing 2016 polls with 2012 election results. Current polls show a high number of undecided voters, and both Clinton and Trump are underperforming compared with 2012. You can see this by the fact that overall, polling data falls along a shallower line than the red diagonal, which indicates equal performance.
In every state in which Trump is ahead, Romney won in 2012. And in every state in which Clinton is ahead, Obama won in 2012 (except for Arizona, where the current median polling margin is quite narrow, at Clinton +1.5%). For now, the 2012 map basically applies. It is highly premature to claim that either candidate is doing differently from his/her party four years ago. Though I must say…Utah, wow.
If you want to work with the data yourself, it is tabulated here.