During a political campaign, a candidate has essentially two equally persuasive paths to take. One is a positive campaign which extols the experience, personal integrity or future goals of the candidate himself. The other is a negative campaign which points out the lack of experience, questionable personal integrity or dubious future goals of his opponent. In order to persuade voters not to vote for an opponent, many politicians use especially negative commercials known as attack ads.
Attack ads must be crafted very carefully to avoid accusations of slander of libel, which means they should only present facts which are on public record. However, attack ads are not required to provide a fair or balanced portrayal of those facts. The point of an attack ad is to present the opponent in an unflattering or hypocritical light, especially when the issue is very important to potential voters. Attack ads on Democratic presidential Michael Dukakis in 1988, for example, portrayed him as soft on crime after a violent criminal he had ordered released as governor, a man named Willie Horton, committed another murder. Dukakis never fully recovered from the negative effects of these attack ads, even if he had a rational explanation for his previous actions as governor.
Some voters can be turned off by the overuse of attack ads, since this negative campaign style is often brutal, even if effective. When 2004 Democratic presidential candidate John Kerry used his military experience as a swift boat commander in Vietnam as a positive campaign issue, a series of attack ads appeared which questioned his honesty, the nature of his injuries and his ability to command others. These attack ads featured veterans who had served with Kerry on the swift boats and believed Kerry's accounts of the events were not entirely factual. Attack ads of this nature may appear mean-spirited to a segment of voters, but they are definitely memorable and effective when presented at a critical time before the general election.
Attack ads essentially force a candidate's opponent to deal with damaging issues in a public way. Sometimes the target of an attack ad will respond in kind with an attack ad of his or her own, or else will find a way to turn a negative into a positive. Some attack ads actually become the jumping off point for a new positive campaign which addresses those accusations. The fact that an opponent can turn a poorly supported attack ad into a positive rebuttal is usually enough incentive for a candidate to use attack ads sparingly and also avoid crossing a moral or ethical line which could hurt the candidate's own perception among voters.