I don't think many people will be surprised that it reached its lowest level in 2016; the intriguing thing is that it was almost as low in 1994 and then rebounded. I wanted to update this partly to see how well it tracked the growth negative feelings about the parties that I wrote about last month. Not that closely: there is a correlation, but that's almost entirely because of the influence of 2012 and 2016.
While looking back at the 2013 post, I see that it was inspired by claims that Mitt Romney's loss in 2012 was because of low turnout among "downscale, Northern, rural whites." Some people have suggested that in 2016, Trump appealed to those voters and they turned out in large numbers. According to the ANES, among non-Hispanic whites who said they voted in 2012, Trump got 53.4% and Clinton got 39.9%; among non-Hispanic whites who said they didn't vote in 2012, Trump got 53.5% and Clinton got 37.4%. That difference is not statistically significant, or even close. Given the small numbers of reported non-voters, there's a lot of uncertainty, but the data doesn't suggest that Trump had a particularly strong appeal to "alienated" white voters. There was one interesting difference: Clinton did substantially worse among blacks who didn't vote in 2012 than among those who did (68.5% vs. 92.5%); Trump, Johnson, and Stein all did substantially better. Although the numbers are very small, the difference is statistically significant.