Only after his poll numbers dropped did Gerald Ford agree to debate challenger Jimmy Carter in 1976.

"I asked Ford, 'Well, why did you agree to the debate?'" said Lehrer. "He said, 'It was my only hope.' He was down and out because of having pardoned Nixon. That's why he was so far down. And he said, 'I needed to do something. And if I could get Jimmy Carter to debate me, I might have a chance.'"

Yet, Ford ended up hurting his chances with this statement: "There is no Soviet domination of Eastern Europe, and there never will be under a Ford administration."

It was a serious gaffe in the Cold War era when the Soviet Iron Curtain extended across Europe.

But it made for compelling TV: Each of the Ford-Carter debates drew in more than 60 million viewers.

The public had spoken, and politicians heard the call: Debates were here to stay.

"No candidate could ever get away without debating in a national form on television now," said Lehrer.

In our highly-partisan era, they're maybe the one thing that can get tens of millions from both parties to sit down and hear what the other side has to say.

And with just the candidates speaking for themselves, all the business of negative advertising and campaign spending that have dominated recent elections fades into the background.

Kathleen Hall Jamieson, a scholar on American elections with the Annenberg School for Communication at the University of Pennsylvania , said debates "dampen down some of the effect of money and politics.

"When we institutionalized debates as a format, we're communicating to the world as well as to the country that we practice what we preach. We believe that there's value in the clash of competing ideas. We believe that the public should judge individuals based on what it is they say and how they argue and how they respond to each other, not simply on the way in which they advertise to us."

Even so, the reality is no candidate steps before the cameras without serious preparation - which is where Brett O'Donnell comes in.

"You know, most candidates look at political debates like 'Jeopardy,' said O'Donnell. "They tend to, you know, want to answer every question and get every question right, thinking that, you know, 'I'll take the economy for $500.' And it's more than that; it's a messaging opportunity."

O'Donnell made tiny Liberty University into a debating power house. Now he teaches politicians debate technique. He's helped George W. Bush and John McCain, and he coached Mitt Romney during the primaries.

"The object is to capture the imagination of both the audience and the press, to make sure your message gets covered," O'Donnell said. "And one way to do that is to have a clever line."

Time and again, Ronald Reagan proved that no one could deliver a one-liner better, like, "Are you better off now than you were four years ago?"