WASHINGTON (AFP) - For sheer political drama, few spectacles can match the sight of two men going toe to toe before tens of millions of television viewers, slugging it out for the most powerful job on Earth.
But as George W. Bush and John Kerry gear up for their first US presidential debate, tentatively scheduled for September 30, the jury is still out on how much impact these high-profile showdowns actually have on the election.
Republican pollster Frank Luntz sees the initial faceoff as the key benchmark. "There is no example ever that the candidate ahead after the first debate eventually loses," he told the political review White House Weekly.
Other experts say that for all the rhetorical fireworks and interminable media analysis, the debates generally do little more than reinforce voter impressions of the candidates and accentuate ongoing trends.
"There have been instances in which it is plausible to think there was an effect," said Kathleen Hall Jamieson, director of the Annenberg Public Policy Center. "Whether or not it affected the outcome we don't know."
The tradition of televised debates began in 1960 with four encounters between Richard Nixon and John F. Kennedy. After a hiatus, they resumed in 1976 and have been a campaign staple ever since.
Many debate moments have gone down in US political folkore: Nixon's unshaven and shifty-eyed look, Gerald Ford's 1976 denial of the Iron curtain in Europe, Al Gore's impatient sighs in 2000.
But only few have been considered critical in helping decide the presidency and these have turned mostly on style over substance. Nixon's sullen appearance against a fresh-faced Kennedy is probably the most famous.
"The classic story is that people who listened to the debate on the radio thought that Nixon won it whereas people who viewed it thought Kennedy did better," said Eric Davis, a noted presidential historian.
In 1980, Ronald Reagan broke open a tight race against Jimmy Carter by brushing off his attacks with a cheery "There you go again" and closing with the killer line for voters: "Are you better off than you were four years ago?"
Experience has also proved the format can make a difference: Bill Clinton used the first "Town Hall" setting in 1992 to score points as folksy and caring in contrast to the patrician, aloof incumbent George H.W. Bush.
The audience for the debates rose from an initial 66 million viewers in 1960 to 80 million in 1980 before dropping steadily to an average of just over 40 million in 1996 and 2000, about 15 percent of the population.
But signs are that the number will be on the upswing for the Bush-Kerry encounters as the climax of an increasingly hard-fought and bitter campaign before the November 2 ballot.
A survey released by the Pew Research Center on Thursday found that 61 percent of registered voters would likely tune in, well up on the 43 percent who said they had planned to watch in the last two elections.
"I think it's going to be very important," Pew Assciate Director Carroll Doherty said of the debate. "It's usually not make or break, but this year people are really locked into this (campaign) in a way they haven't been since 1992."
The US Commission on Presidential Debates has proposed three debates: one September 30, a second on October 8 and a final session October 13. Negotiators for both sides are hashing out details amid reports Bush hoped to skip the second bout.
Experts agreed that once the candidates hit the podium, the burden was on Kerry to prove he can measure up as a commander-in-chief, to stake out differences with Bush on domestic issues and articulate a clear policy on Iraq.
"It's always more important for the challenger because he has to pass over the threshhold that establishes you're an acceptable leader," said Jamieson.