What is driving the decline in swing voters? Smidt shows that voters are increasingly cognizant of the sharp differences between the Republican and Democratic parties. In fact, a politically inattentive and unengaged American today is as likely to perceive important differences between the parties as a very engaged American was in 1960. See this graph:
Smidt goes on to show that people who think the parties differ tend to have opinions, and more consistent opinions, about the presidential candidates. Taken together, all three of these factors — perceiving the parties as different, having opinions about the candidates, and having consistent opinions — are related to the decline of the swing voter.
In short, there is less reason to “swing” when only one party is attractive to you.
Smidt sums it up like this:
By making it easy for Americans to recognize party differences, polarization has reduced ambivalence and indecisiveness and provided a strong and consistent ideological anchor to Americans’ presidential preferences across time, even for independents and the less aware.
One implication, Smidt notes, is that American voters should be less responsive to election-year forces, like shifts in the economy or other important events. Another is that politicians have less incentive to appeal to swing voters and more incentive to appeal to their loyal supporters.
Of course, shifts in the economy and swing voters could be decisive in 2016 if the election is close enough. But most American voters will supply little in the way of drama or excitement. Predictable partisanship is increasingly the norm.