"Aside from the conventions, the debates are the only time most Americans are going to watch McCain and Obama for an extended period of time -- a period of time that allows them to make judgments about their character, their sense of self and how they handle themselves and their adversaries in stressful situations," said former White House political director Sara Taylor, a Bush-Cheney deputy strategist in 2004.
Some presidential debates have had an impact when elections have been very close like this one, and can be game changers.
During the 1960 presidential debate between Kennedy and then-Vice President Richard Nixon -- where famously people on the radio thought Nixon had won while voters who watched the debate on television said Kennedy had won -- Nixon was widely assumed to have a leg up on foreign policy issues.
"That debate was pivotal in elevating Kennedy to Nixon's level and overnight diffusing the experience argument," Smith said.
However, Smith cautioned against putting too much emphasis on who is perceived to come out on top after the debates.
"Four years ago all the polls indicated that Sen. Kerry won all three debates," Smith said, "and it didn't help him on Election Day."