John McCain is hammering Barack Obama over his association with former 1960s radical William Ayers in a new TV ad.

The ad says: “When convenient, he worked with terrorist Bill Ayers. When discovered, he lied.”

The commercial is arguably McCain’s sharpest yet, and it uses Obama’s link to Ayers to assert that Obama has “blind ambition” and “bad judgment.”

McCain’s campaign says the ad will run nationally.

The Associated Press and other news organizations have reported that Obama and Ayers are not close but that they worked together on two nonprofit organizations from the mid-1990s to 2002. Ayers also hosted a small meet-the-candidate event for Obama in 1995 as he first ran for the state Senate.