DENVER (AP) -- Barack Obama and a conservative group have fired off dueling letters to the Justice Department.
The two sides are escalating their fight over the group's TV commercial linking Obama to a 1960s radical.
The Obama camp argues that the organization, the American Issues Project, is violating the law. For its part, the group is citing a Supreme Court ruling to argue it is allowed to air the ad, which links Obama to 60s radical William Ayers.
Ayers was a founder of the Weather Underground organization that claimed responsibility for a series of bombings, including nonfatal explosions at the Pentagon and U.S. Capitol, four decades ago.
Ayers is now a professor at the University of Illinois at Chicago. He and Obama served together on the board of a Chicago-based charity. Obama left the board in 2002.
(Copyright 2008 by The Associated Press. All Rights Reserved.)