Bryan Caplan (The Myth of the Rational Voter) says, Watch the Platforms, Not the Winner:
Puzzle: If you look at voting behavior, education does little to make people more Democratic or more Republican. So what difference does it make if people acquire more sensible views about policy, if it doesn’t change their vote?
What I question is that we should be very interested in the differences between presidential candidates in the first place. In our competitive democracy, the candidates wind up being pretty similar in any case. The real problem of democracy is bipartisan agreement on foolish policies.
So how can more reasonable beliefs about policy sway political outcomes? The answer is surprisingly simple. When public opinion gets more reasonable, both parties adjust their positions to avoid giving the competition an edge. For example, the U.S. public is markedly less protectionist than it was in the ’70′s, leading both parties to become markedly less protectionist than they used to be. The identity of the winning party might make a marginal difference; but this difference is muted by the fact that politicians want to get behind whatever happens to be popular.