Looks like the Swifties attack ads on Kerry are beginning to have an effect. How much remains to be seen.
Seems to me that people who despise Bush won't be persuaded by the ads to vote for him. Why should they? The ads are about Kerry's alleged unfitness for the Presidency, not about Bush.
Conversely, people who love Kerry, not that there's a huge number of them, won't listen to the ads at all. No effect here, either.
Maybe the greatest impact of the ads will be to persuade some people, number unknown, who had formerly intended to vote for Kerry to NOT cast their ballot for him.
IOW, the net effect of the ads will be to cost Kerry votes which will not then go Bush. Bottom line, if this scenario is correct, is that Bush picks up a greater percentage of the Presidential vote because of the ads causing some voters to drop their support for Kerry.
Sharp-eyed vote analysts will pick apart the results comparing numbers of ballots cast for each race (Senate, House, State, Local, etc.). Look for a discrepancy in number of ballots cast for President and other offices to see if the ads had an effect.