A poll by the Investor's Business Daily puts Bush ahead of Kerry by three points -- five, if Nader stays in the race. Some had hoped that the Wall Street Journal poll, which also put Bush ahead, was an anomaly. It wasn't.

Kerry was six points ahead in a CNN poll conducted March 5-7, and nine points ahead in an ABC News/Washington Post poll conducted at the same time. Now he's behind.

What's changed?

Bush started airing commercials showing 911 imagery. These commercials were denounced by pundits, firefighters, and families of the victims. Nevertheless, the ads have worked.