WASHINGTON — The troubled presidential debate for third party candidates scheduled for Sunday at Columbia University in New York was canceled Friday after none of the four candidates had committed to the event.

"Due to circumstances beyond our control, several of the candidates decided not to participate in the debate at the last minute," said Lauren Salz, a student with the Columbia Political Union, which was hosting the debate.

Independent Ralph Nader, Libertarian Party nominee Bob Barr, Green Party candidate Cynthia McKinney and Constitution Party nominee Chuck Baldwin were expected to participate in what was billed as a "historic" event.

Barr claimed a conflict while McKinney opted for an online debate originally scheduled for that evening. Baldwin was reluctant to travel to New York. Nader was willing to participate, say aides, but, seeing the debate falling apart all week, held back.

McKinney, it turns out, also had another reason for staying in her hometown of Atlanta, said her running mate, Rosa Clemente. McKinney is attending the Black Panther Party annual reunion.