Those of you who follow closely the impact of changing demographics on election results are likely to find interesting tidbits in Sean Trende‘s recent guest column for “Larry J. Sabato’s Crystal Ball” at the University of Virginia’s Center for Politics. Trende responds to critics who question his earlier findings that Democrats’ increasing success among nonwhite voters has been accompanied by deteriorating support among white voters.

We all agree that non-whites are a growing share of the population, and that they are heavily Democratic (Abramowitz and Teixeira suggest they are increasingly so). If whites’ overall party ID had remained constant, we would expect the influx of non-white, Democratic voters to gradually increase the portion of the electorate that identifies with Democrats. Instead, Gallup finds this: Party identification ebbs and flows in predictable response to national events, but basically does so around the same midpoints. …

… None of this should be surprising. Whites have become more prosperous over the past 50 years, and income still correlates with Republican voting habits (for Hispanics, non-Hispanic whites and, to a lesser extent, African Americans). Moreover, Democrats’ decision to embrace policies aimed at their “coalition of the ascendant” cannot be viewed in a vacuum. A case in point is Arizona, a state where Mitt Romney ran about as well as George W. Bush, despite a less favorable national environment. The Hispanic vote there has grown and, given a state GOP that stands as a poster child for how not to attract Hispanic voters, has moved sharply toward Democrats. But the Democrats’ stance on immigration isn’t particularly popular among whites, and whites, especially whites without college degrees, have shifted toward Republicans, resulting in no net change.

The bottom line is that political scientists have been reasonably successful at predicting elections based on a few basic factors. None of them, to my knowledge, includes a demographic variable. If the only relevant demographic change were the growth in the non-white vote, we’d expect these models to take on a pro-Republican bias over time, as a pro-Democratic variable that the models fail to account takes on increased salience.

But models like Nate Silver’s famous FiveThirtyEight model, the Hill/Sides/Vavreck model and many others called the election pretty well, without reference to demographic changes. …

… Any one of these observations, standing alone, would stand as reasonable evidence that the Democrats have been shedding white voters over time. Combined, they’re pretty compelling. The Democrats are reaping the benefits of our increased diversity. But they’re paying it back with an increasingly poor showing among whites.