Bill Clinton's face morphs into Sen. John McCain's.
Pollution bellows out of Texas smokestacks.
A narrator explains the importance of abortion rights over the image of the Supreme Court's majestic facade. Each image has run across voters' television screens in an attempt to influence the presidential debate. As actual voting nears, candidates are inching closer to negative advertising, but the nastiest ads by far have been produced by outside groups with their own agendas. Sometimes campaigns welcome them, but in many cases, even the candidate who is ostensibly helped is wary. Unlike their own ads, they have no control over what many outside groups put on the airwaves.