Much is said of the gaffes, zingers and awkward gestures that have lurked in presidential debates. But only a handful of significant missteps have occurred in over half a century of television-era debates.
And few, if any, have been decisive game changers.
The stakes are clearly high as President Barack Obama and Republican challenger Mitt Romney square off in Denver in the first of three showdowns.
But unlike election results or prize fights, there are seldom knock-out punches or clear-cut winners in debates. Sometimes it takes days for a consensus to emerge - if ever.
Richard Nixon's haggard appearance vs. John F. Kennedy's vigor is widely cited as contributing to a Kennedy victory in the first 1960 debate. But polls showed that was true mostly for those who watched it on TV, while those listening to the radio generally picked Nixon as victor. And Nixon did better in three later debates.
Few gaffes are as striking as President Gerald Ford's 1976 erroneous claim that that Eastern Europe was not under Soviet domination. But Ford had held his own in an earlier debate, and many other factors contributed to his defeat by Jimmy Carter.
Michael Dukakis in 1988 and John Kerry in 1996 were generally deemed superior technical debaters - but both lost to a George Bush.
Obama was generally judged to have bested John McCain in the three 2008 debates and hopes to do so again over Romney.
But four years ago Obama could use the weak economy to his advantage. Now he can't.
Both camps usually seek to lower expectations while praising the debating skills of their opponent - just as the Obama and Romney teams are doing now. And, if they stick to that tradition, they'll also both claim victory - no matter what transpires - when it's over.