Former Canadian Ambassador to the U.S. McKenna moderates a discussion on global affairs between former U.S. Presidents Bush and Clinton in Toronto

Former Canadian Ambassador to the U.S. Frank McKenna (L) moderates a discussion on global affairs between former U.S. Presidents George W. Bush (C) and Bill Clinton (R) at a convention center in this handout photo released by TD Bank from the event in Toronto, May 29, 2009. This is the first time the two presidents have participated in a joint event together. REUTERS/TD Bank Financial Group/Handout (CANADA POLITICS) FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS