The Changing Electorate

One reason it's difficult to read midterm elections as reflecting shifts in the "national mood" is that the actual set of voting people is quite different. According to exit polls, for example, the relative proportion of youth voters and senior voters shifted quite dramatically:

That under-30 bracket still strongly backed Democrats by a 57-40 margin, turning only somewhat more skeptical of the party. But it also shrunk precipitously as a share of the voting public. But Americans didn't react to "liberal overreach" by suddenly aging four decades in the span of eighteen months. Older people are just more inclined to stay engaged with lower profile elections.