Just to add to Andy’s post, here’s a very useful essay from City Journal by John M. Murtaugh, a law professor and NY city councilman.:
During the April 16 debate between Hillary Clinton and Barack Obama, moderator George Stephanopoulos brought up “a gentleman named William Ayers,” who “was part of the Weather Underground in the 1970s. They bombed the Pentagon, the Capitol, and other buildings. He’s never apologized for that.” Stephanopoulos then asked Obama to explain his relationship with Ayers. Obama’s answer: “The notion that somehow as a consequence of me knowing somebody who engaged in detestable acts 40 years ago, when I was eight years old, somehow reflects on me and my values, doesn’t make much sense, George.” Obama was indeed only eight in early 1970. I was only nine then, the year Ayers’s Weathermen tried to murder me.