In 2004, the George W. Bush campaign produced one of the most devastating attack ads ever run. The "Windsurfing" ad was a 30-second spot that depicted Democratic presidential candidate John Kerry as a "flip-flopping, windsurfing elitist," who changed his positions to try to increase his support from voters. Kerry was shown windsurfing to the left and right, to symbolize his supposedly changing stances on the war in Iraq, and funding for troops, educational reform, and medicare premiums. These and other ads might have made the difference in President Bush's narrow margin of victory, which was 3 percent in the popular vote and 6 percent in the Electoral College. Click on this link to view the "Windsurfing" ad: https://www.youtube.com/watch?v=pbdzMLk9wHQ
Now, in 2011, the Democratic National Committee has already run a similar 30-second spot ad, directed against a candidate who has not even been nominated yet (and may not be): Republican Mitt Romney. The "Trapped" ad pits "Mitt vs. Mitt" on abortion and health reform, stating that Romney (like Kerry) is "willing to say anything" to get elected. Click on this link to view the "Trapped" ad: https://www.youtube.com/user/DemocraticVideo#p/u/0/CUOM9QvhG5I
Such attacks can be effective, since they can get voters to question the "character" of candidates.