Texas billionaire Harold Simmons, a major backer of Republican John McCain's presidential campaign and Swift Boat Veterans for Truth four years ago, is the sole donor to an advertisement attacking Democrat Barack Obama over his relationship with one-time radical activist William Ayers.

A campaign finance filing shows Simmons donated the entire $2.8 million being spent by a new group, American Issues Project, to air the commercials in Ohio and Michigan next week.

Ayers was involved in a group took credit for bombings that included nonfatal blasts at the Pentagon and U.S. Capitol four decades ago. After he surrendered in 1980, charges against him were dropped because of prosecutorial misconduct.

In April, Obama said that he "deplored" Ayers' actions in the 1960s and that "by the time I met him, he is a professor of education at the University of Illinois."

Among the Ayers-Obama ties, the two served together on the Chicago Annenberg Challenge, a nonprofit educational reform organization. (Its records will be made available to the public Tuesday, the University of Illinois said Friday.) They also served together on the board of the Woods Fund, a Chicago-based charity.

The ad says Obama and Ayers served together "on a left-wing board. Why would Barack Obama be friends with someone who bombed the Capitol and is proud of it?"

McCain's campaign has denied any involvement in the ad. Under federal law, it would be illegal for McCain to be involved.

A board member of the American Issues Project, Ed Failor Jr., worked for McCain's campaign last year.