The presidential debates are generally considered the last big opportunity to move voters before the election. They offer rare moments for Americans to do some head-to-head comparison shopping between two candidates on the same stage discussing the issues.

And yet, according to the numbers, the debates have done little to change the fundamental structure of recent presidential races. Looking at pre-debate NBC News/Wall Street Journal presidential polls and the final election results since 1992, there is only one campaign where the debate may have made a serious difference — 2000.

In every other case, the candidate that led going into the debates wound up winning on Election Day.