Political debates are as old as politics itself, and experts say everything from image to rhetorical style play into who wins.
With a close race, whoever wins the presidential debate could win the election. Roughly one-third to one-half of voters wait until after the debates to make up their minds.
"(Voters) can evaluate the candidates firsthand rather than filtered," said Bruce Altschuler, professor of political science at the State University of New York-Oswego.
Robert Denton Jr., professor of communications at Virginia Polytechnic Institute and State University, said that for a debate to be effective, voters already must be informed generally of the issues.
"The primary effects of (these) debates are not to change someone's mind, but to serve as a reinforcement," he said.
But people who already have their minds set about a candidate will be harder to sway, he said. Research has shown that undecideds look at debates as their deciding factor.
Denton predicts 60 million people will watch the debates this year, as opposed to the almost 47 million who watched four years ago.
Experts differ on the secret to a successful debate - presenting a likable image or being on the right side of an issue for the voting public. Denton said he believes the image in a debate is stressed beyond the actual issues.
He pointed to the 1992 debate between Bill Clinton and George H.W. Bush, saying that Bush's glance at his watch indicated to the audience that he must be bored and out of touch with his presidency. At the same time, he said, Clinton appeared empathetic and personable.