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.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

And, to be fair about 2000, Democrat Al Gore actually did get more votes than Republican George W. Bush (but lost the Electoral College), so technically — where the popular vote is concerned — the numbers above show a perfect 6 for 6. The candidate that led in the poll going into the debate period won the election.

Does that mean debates never matter? No. They give the media a chance to hold candidates' feet to the fire. They give voters a way to see how candidates handle the pressure of a big audience in a prize fight atmosphere. They give the candidates a chance to close the deal or one last chance to raise questions about their opponent.

But changing an election? The lone debate between Ronald Reagan and Jimmy Carter in 1980 is often cited as an example of one that did, but the evidence for that isn’t completely clear.

Gallup polling showed Carter with a lead over Reagan just before the October 28th debate and Reagan wound up winning by 10 points. But an analysis of a collection of polls over the course of the year from the political science blog The Monkey Cage shows that Reagan actually led by a solid margin from June going forward to Election Day.

There are debate moments people remember. The 1988 debate between George H. W. Bush and Michael Dukakis featured Dukakis’s cool answer to what he would do if he found his wife had been raped and murdered. There was the time in the 1992 town hall debate between Bill Clinton and Bush, when Bush looked at his watch, seemingly bored. And there were Al Gore’s audible sighs during his debate with George W. Bush. But poll numbers suggest all those memories did nothing to change the shape of those races.

Considering the high-stakes moments that the debates create one might expect them to matter more to the bottom line, but remember debates happen late — very late — in the campaign. By the time those candidates hit the stage most voters have seen and heard from them over and over again on TV, online, in the newspaper and on the radio. Voter’s images of the candidates are usually well-formed.

Of course, that’s doubly true in modern presidential campaigns, where another seems to start as soon as the current one ends. Look at this year’s nominees.

Hillary Clinton announced she was running for president in April of 2015, some 17 months ago. Donald Trump was a later arrival, announcing in June of 2015, only 15 months ago. Both candidates have been on primary debate stages. They’ve spoken at countless rallies. They’ve each had numerous public missteps in this election cycle.

And, this year in particular, the two nominees are well-known commodities. Their images and foibles have been gracing our TV screens for decades. Since the early 1990s for Clinton. Since the 1980s for Trump.

That’s not to say nothing will happen Monday night. The candidates will be on stage, face-to-face. And considering their apparent dislike for each other there may be fireworks and many memorable moments. But history and the numbers say the race Tuesday morning probably won’t look much different from Monday.