Candidates for political office — from sheriff to president — expect to be pounded by attack ads. Even founding fathers Thomas Jefferson and John Adams hurled insults at each other in the presidential election of 1796. Today, radio, TV and Internet attack ads, spread virally by social media, can distort the truth, demonize opponents and violate civic taboos. But they work. They're controversial because they use subtle — and often not-so-subtle — suggestions to plant slanderous information in voters' minds. Here are 10 of the most controversial political ads from the past 50 years.