I think the dynamics of the presidential race in the last few weeks diminished Romney votes because of the assumption that he was going to win anyway. Many voters are more comfortable casting negative votes than positive ones, because the latter involve a greater degree of responsibility for the result. Combined with Romney's apparent lead (until Sandy), Romney's greater specificity on economic issues placed greater responsibility on those who voted for him, whereas Obama's vagueness provided a more comfortable place for those who don't want to feel responsible for their votes.