After Ronald Reagan's poor performance and questionable command of the facts in his first presidential debate against Walter Mondale in 1984, critics wondered if age was starting to rob the 73-year-old president of the mental capacity he needed to lead the free world.
Reagan kept mangling facts in a second debate. But even so, he disarmed his critics and his opponent with the quip, "I will not make age an issue in this campaign. I am not going to exploit, for political purposes, my opponent's youth and inexperience."
The remark dominated the news cycle and rolled off pundits' tongues long after Reagan cruised to a landslide victory on Election Day.
As President Bush and John Kerry drill on the issues before tonight's debate on foreign policy and homeland security, they likely are burnishing zingers and ripostes that they hope will neatly encapsulate their own messages or indelibly stain their opponent through Nov. 2.
Perhaps their best material even could stick in political lore as vividly as Reagan's "There you go again" dismissal of Jimmy Carter in 1980, or Lloyd Bentsen's "You're no Jack Kennedy" putdown of 1988 vice-presidential aspirant Dan Quayle.
Voters tend to watch presidential debates to get an overall impression of each candidate as a person or leader, observers say. But soon afterward, the soundbite-style nature of modern media coverage can amplify effective gaffes or quips, and maybe even change initial perceptions of who won the debate.
Not everybody is pleased by the phenomenon.
"The problem with the presidential debates, I think, is that it really has become much more spectator sport than an effort to educate the voters on the issues," says Marie Danziger, director of the communications program at Harvard University's John F. Kennedy School of Government.
The boldest debate quips are rarely, if ever, off the cuff.
"Most of the things that we remember as the key debate moments have been scripted," says Alan Schroeder, a professor at Northeastern University in Boston and author of Presidential Debates: Forty Years of High-Risk TV. "'There you go again,' 'I won't exploit my opponent's youth and inexperience,' 'You're no Jack Kennedy.' Those were all practiced in advance."
The candidates are also likely practicing to avoid going too far out on a limb, thus avoiding debating gaffes that have long thwarted candidates — such as Al Gore's awkward sighs in 2000, George Bush's glances at his watch in 1992, Gerald Ford's insistence that "there is no Soviet domination of Eastern Europe" in Cold War-era 1976 and Richard Nixon sweating next to a relaxed John F. Kennedy in 1960.
"I think Bush and Kerry are pretty evenly matched, so I don't know if this year will produce any knockout winners," Schroeder says. "My guess is that each of them will probably wage a fairly careful and restrained rhetorical strategy."
Still, Schroeder says, "I'd be willing to bet the deed to my condo that Bush will have some quip ready about Kerry's alleged 'flip-flops.' "
White House communications director Dan Bartlett may have let slip a Bush zinger when on Monday he cited a catchphrase from the game show Who Wants to Be a Millionaire in a conversation with reporters.
"Senator Kerry keeps wanting … to say, 'Now, this is really my position,'" Bartlett said. "The question needs to be asked is: 'Is that the final answer?'"
Schroeder believes Kerry might hit Bush with "a one-liner or two based on an economic theme, sort of an updated version of Reagan's 'Are you better off now than you were four years ago?' from 1980."
Kerry would likely use such a line during the second presidential debate on Oct. 8, when the discussion will be open to topics beyond the foreign affairs and homeland security that will be covered tonight, or during the Oct. 14 debate covering domestic issues. The vice-presidential debate on Oct. 5 will be open to all topics.
In such debates, says Danziger of Harvard's Kennedy School, it is useful for debaters to encapsulate their thoughts into tidy statements.
"Zingers are important in all public speaking," Danziger says. "I teach my students all the time that one of the most important parts of the speech is a short, dramatic statement of your bottom line, because that's what listeners will remember."
She discourages students from political-style attack zingers, though she understands they may be a symptom of political debates' emphasis on winning public office. Academic debates, on the other hand, can be more focused on ideological persuasion.
"I tell my students that their primary goal should be to provide citizens with the information they need to make the decisions that will affect their lives," Danziger says. "I think most people will agree that the presidential debates have a goal that's quite different from that."
Even if the candidates have what they think are surefire putdowns in store, there may be other arguments against deploying them.
"If they're too sharp or too personal, they can backfire and make the person telling the joke look worse than the target of the joke," Schroeder says.
Such may have been the case in a 1976 vice presidential debate, when Bob Dole relentlessly attacked his Democratic counterpart Walter Mondale.
"He made a crack about Walter Mondale's makeup at one point," Schroeder said. "It was a personal, barbed sort of comment … that went beyond fellowship."
Another Dole remark decried American deaths in "Democrat wars," such as World War I, World War II and the Korean War, prompting Mondale to say, "I think Senator Dole has richly earned his reputation as a hatchet man tonight."
One-liners also can come across as too soft or unoriginal, particularly as viewers have come to expect them.
Mondale still is remembered for a 1984 Democratic primary debate quip in which he asked of an opponent's positions, "Where's the beef?" quoting a popular catchphrase from an advertising campaign of the day.
But perhaps fewer people recall that Massachusetts Gov. Michael Dukakis initially got chuckles with a knock-off in 1988, referring to a duplicitous ad pitchman in his comment that Vice President George Bush threatened to become "the Joe Isuzu of American politics." In the same debate, Bush called one of Dukakis' answers, "about as clear as the water in Boston Harbor."
"It was so obvious that they just sort of landed with a thud," Schroeder says. "Certain debaters are more adept at detonating these lines than others. Ronald Reagan was a master at it because he could speak one of these pre-scripted lines and make it sound off-the-cuff and spontaneous."
Schroeder is not certain Bush and Kerry — though both strong debaters — have what it takes to deliver a line for the ages.
"Kerry doesn't try that many jokes because it's not really natural to him," Schroeder says. "You can see the gears sort of turning when he's trying to do one of these things that he's been told to do. … He can't make it sound like it's something he just thought of."
"Bush's issue is sort of that he's so on message, you don't feel like you're getting the answer to the question," Schroeder adds. "You're getting the answer that he rehearsed."
ABC News' Terry Moran contributed to this report.