"How is the money spent? [Mainly] an ever-increasing volume of negative, distorting and ideologically tinged advertising about opposing candidates and parties. Contrary to what many believe, the central effect of such negative advertising isn’t to move voters from supporting another candidate to backing yours, as Mitt Romney and his allies have discovered during this primary season. The main effect is not even to move undecided voters into your column. No, the real effect of negative advertising is to energize and solidify support among your ideological base while turning everyone else off to the other candidate, the campaign and the entire electoral process. Negative advertising isn’t about changing minds; it’s about altering the composition of the voter pool on Election Day by turning moderate voters into non-voters."
Steve Pearlstein, “Turned off from politics? That’s exactly what the politicians want.”
Forget about “undecided” voters. They don’t exist anyway (they’ve already decided). Follow the money instead. It’s all about the composition of the voter pool.
EDIT: Link and parentheses added.