Obama responds to ad tying him to '60s radical

DENVER (AP)-- Democratic presidential contender Barack Obama has quietly begun airing a television commercial countering an outside group that is spending $2.8 million in an attempt to highlight his relationship with a former 1960s radical.

The 30-second TV spot is a response to an ad by the conservative American Issues Project, a nonprofit group that questions Obama's ties to William Ayers, a founder of the Weather Underground organization that took credit for a series of bombings, including nonfatal explosions at the Pentagon and U.S. Capitol four decades ago.

''With all our problems, why is John McCain talking about the 60s, trying to link Barack Obama to radical Bill Ayers,'' the Obama ad states. ''McCain knows Obama denounced Ayers crimes, committed when Obama was just 8 years old.''

Though McCain is not airing the anti-Obama ad, the group that produced and paid for it is financed by a McCain fundraiser and one of its board members is a former consultant to McCain's presidential campaign.

The American Issues Project ad has already aired about 150 times in Pennsylvania, Ohio, Virginia and Michigan, according to Evan Tracey, head of TNS Media Intelligence/Campaign Media Analysis Group, an ad tracking firm.

Obama's response was running at least in Youngstown, Ohio, Tracey said. The Obama campaign did not announce the release of the ad, even though it publicly disclosed another anti-McCain ad released Monday.

Ayers is now a professor at the University of Illinois at Chicago. He and Obama live in Chicago's Hyde Park neighborhood and served together on the board of the Woods Fund, a Chicago-based charity that develops community groups to help the poor. Obama left the board in December 2002.

Obama also was the first chairman of the Chicago Annenberg Challenge, a school reform group of which Ayers was a founder. Ayers also held a meet-the-candidate event at his home for Obama when Obama first ran for office in the mid-1990s.