Negative advertising and smear campaigning have been staples of American politics for nearly two centuries. Some historians trace the roots of the practice back to the 1828 presidential election, during which John Quincy Adams reportedly claimed that his opponent, Andrew Jackson, was a cock-fighter and a cannibal with a prostitute for a wife. Jackson cruised to victory despite those charges.
While the product of negative campaigning is often not pretty, the conventional wisdom is that it works, whether voters choose to admit it or not. As is the case with most of politics' darker arts, however, there is a line that many say shouldn't be crossed. While the bar for what is considered acceptable has been set high, below is a list of particularly controversial attacks that have made waves in the political arena for going too far. Which are in bounds, and which are just par for the course?