Since the watershed post-Watergate election of 1976, the American voter has picked the more likeable of the two Presidential candidates without regard to their policies. (Winner in bold.)
1976 Ford vs. Carter
1980 Reagan vs. Carter
1984 Reagan vs. Mondale
1988 Bush vs. Dukakis
1992 Bush vs. Clinton
1996 Dole vs. Clinton
2000 Bush vs. Gore
This is obviously just a theory and may well have more to do with the familiarity that voters now have with the candidates' images via television than anything else -- like, say, Watergate.