For a "TODAY" exclusive, Jenna Bush Hager has sat down with each of the four former U.S. presidents. During their sitdown, Presidents Joe Biden, 83, Barack Obama, 64, Bill Clinton, 79, and her father, George W. Bush, 79, shared a message for the American people ahead of the nation’s 250th anniversary in July. Bush Hager shared Monday on "TODAY" that she spoke individually with each at a private event over the weekend in Philadelphia hosted by the History Channel. The event, named “History Talks,