ou see what you expect to see. The voters have come to expect presidential debates, but they think they know what they'll get.
Previously-arrived-at opinions tend to be confirmed. Debates tend to ratify what you already thought. Candidates who acquit themselves well can shore up their base, allay doubters' concerns, and make inroads on the great gray blob of undecideds.
Stumble, fumble, or come across as too nasty or too tightly wound, and you depress your base turnout, lose potential contributors who before writing the check were waiting for a glimpse of you under fire, and energize those who wish you ill, especially candidates for lesser offices lower down on the other party's ticket.
Think of the confrontation as two howling, sullen mobs arrayed across a stubbled battlefield, as at the Battle of Agincourt in the Hundred Years' War. Arrows flying, horses neighing, drums beating, and confusion reigning along both fronts, the tumult is mind-boggling, and the need for steady nerve is paramount. Debates are gladitorial facedowns, much more theater than political science, much more World Wrestling Federation than academic.
Agincourt comes to Dorchester Bay on Oct. 3 with the first Gore-Bush face-off of the campaign. It's the first of three, but in the past the initial confrontation has tended to be most widely watched, and therefore most significant for the billion-dollar election efforts unrolled by both major parties. Generally, a challenger gets more lift from a debate than an incumbent, or a vice president seeking to move up. That was true in the four Kennedy-Nixon debates of 1960, the first of the television age.
There was a 16-year gap before public pressure forced Gerald Ford and Jimmy Carter into three debates. There have been 17 in all, and their impact is charted in a new book by Northeastern University assistant professor Alan Schroeder, ''Presidential Debates; Forty Years of High-Risk TV.''
Because of the way broadcasters cue up sound bites from past debates, journalists tend to make too much of the verbal putdown. That obscures the more complex and cumulative effect of appearances, self-confidence, thoughtfulness, ''nice-guy-ness.'' So we recall lines like Lloyd Bentsen's to Dan Quayle: ''I knew Jack Kennedy, and you're no Jack Kennedy,'' or Ronald Reagan's ''There you go again'' riposte to Carter's scathing assessment of Reagan's grasp of health care issues.
My own list of memorable moments from debates past:
Most Awkward: the 27-minute delay in Philadelphia's '76 debate when the power failed in the studio and we in the audience were kept writhing in our chairs by Secret Service agents while Ford and Carter stood frozen in anxious amber.
Biggest Gaffe: Ford's goofy declaration in 1976 that Poland was not under Soviet domination. That crystallized the Nixon haters' loudest objections to genial Gerry, that he was dumb. Which he is not.
Blown Answer: Michael Dukakis in his second 1988 debate with George Bush. The Duke had edged Bush by 45 percent to 36 in the ABC poll after their first debate. But in the second, Bernie Shaw asked him what if Kitty Dukakis were raped and murdered, would he still be against the death penalty? Dukakis's bland and programmed reply went down badly everywhere. The Democrat ''went into the hole on the very first question and never climbed out,'' I wrote that night. ''As the night progressed, Bush got better, and the Duke got worse.''
Unlucky Break: Unknown to any but his intimates, Dukakis awoke that morning in Los Angeles with no voice. Laryngitis left the candidate groggy and croaky, with a 103-degree fever, prompting frantic phone calls back to his doctor in Milton. Hot tea, honey, and a quick referral to an LA doc put Dukakis in shape to go on that night; cancellation would have been a disaster. But his reply to Shaw was an even bigger disaster, effectively burying the Democrats' chances. He lost big states by tiny margins of 1, 2, or 3 percent.
Worst Time to Look at Your Watch: Bush in '92 when the camera caught him peeking at his wristwatch while Bill Clinton was mopping the floor with him for being aimless and out of touch with the voters' economic pain.
Most Baffling Digression: The Gipper getting lost on the Pacific Coast Highway in his meandering and mangled closing statement in his debate against Walter Mondale in '84. The later revelation that Reagan has Alzheimer's disease prompted some evaluators to go back to that debate to see if his illness was presaged then. Campaign chief James Baker tried to shield his vulnerable boss by claiming Reagan's briefers had ''brutalized'' the boss with their pesty preparations.
Most Freudian Moment (OK, this was a VP event): When James Stockdale, the hapless running mate of Ross Perot, debated Al Gore and Vice President Dan Quayle in '92, the former POW and Navy hero opened with ''Who am I?'' and ''What am I doing here?'' which invited ridicule and made his patron, Perot, look even more wacky.
Best Jug-Earred Soundbites: Jousting with Bush and Clinton in '92, Perot staggered Bush by jibing, ''I don't have any experience in running up a 4 trillion dollar debt,'' and later defending his scheme to raise gas taxes by cracking, ''If there's a fairer way, I'm all ears.''
There may be 100 million people tuning in to the UMass-Boston debate. On the outside looking in will be Pat Buchanan and Ralph Nader and the others who found their way onto various state ballots. We know this about presidential debates, and massive national television audiences: If you build it, they will come.
David Nyhan is a Globe columnist.
