Key debates in US presidential history

Republican presidential nominee Donald Trump speaks during a rally at the Sun Center Studios in Aston, Pennsylvania

Monday's debate between Donald Trump and Hillary Clinton is likely to be the most watched in US presidential history. But will it be as consequential, controversial or instructive as some of the debates of the last half century? Kennedy-Nixon This is where it all began. Fifty-six years ago in Chicago a young, relatively unknown Massachusetts senator and the incumbent vice president Richard Nixon sat below the studio lights for the first ever general election debate. It turned out that while John F. Kennedy was the underdog, he was also the right man for his time. Kennedy appeared as telegenic as Nixon appeared sweaty and unwell -- the vice president had recently been hospitalized and refused to wear stage make-up. Kennedy's debate victory turned out to be more important than anyone imagined. "Kennedy's mastery of the medium helped him convert a slight deficit in the polls to a squeaker of an election victory," said Lance Tarrance of Gallup. Carter-Ford If Kennedy showed the consequence of a good debate performance, then Gerald Ford showed the consequence of a slip up. Al Gore famously drew fire for sighing repeatedly in a debate with George W Bush. His father, George Herbert Walker Bush, was painted as uninterested for looking at his watch while debating Bill Clinton, but neither mattered too much. In 1976, however, when Gerald Ford faced Georgia governor Jimmy Carter, he made a gaffe that may have cost him the presidency. When the topic shifted to the Soviet Union's actions in Europe, Ford -- almost inexplicably for a president who just a year earlier signed the Helsinki Accords -- declared "there is no Soviet domination of Eastern Europe." Taken aback, the moderator interjected and asked for clarification. But Ford refused to admit his error and back down. Polls from the time showed Ford actually did very well in the debates overall -- narrowing the gap with Carter from twenty points before the debates to six after. Without that stumble, he have might even have passed Carter and won the election. Obama-Clinton Some debates have proven important not because they were decisive, but because they were instructive. In a 2007, Democratic primary debate with Hillary Clinton, Barack Obama would give an answer that would serve as a guide his foreign policy in the White House. Obama was asked: "Would you be willing to meet separately, without precondition, during the first year of your administration -- in Washington or anywhere else -- with the leaders of Iran, Syria, Venezuela, Cuba and North Korea, in order to bridge the gap that divides our countries?" "I would," came the arrestingly frank response that was painted as a gaffe at the time. "The notion that somehow not talking to countries is punishment to them -- which has been the guiding diplomatic principle of this administration -- is ridiculous." After eight years in office Obama has only met the leaders of two of those countries -- Cuba and Venezuela -- but rapprochement with Iran, Cuba and Myanmar are seen by the White House as three of his main foreign policy achievements. Lincoln-Douglas Like James Joyce's Ulysses, more people have referenced the 1858 Lincoln-Douglas debates than have actually read them. But over a century-and-a-half, the seven marathon encounters between Abraham Lincoln and Stephen Douglas have become a byword for substantive political discourse. Touching on slavery, war and morals, each began with an hour-long address, followed by a 90 minute rebuttal, followed by a 30 minute counter-response -- positively Socratic compared with today's commercial-break-laden affairs. In fact, the Lincoln-Douglas debates were not presidential debates at all, the pair were competing for a US Senate seat for Illinois. And clocking-in at three hours per candidate, they were not exactly material for primetime TV either.