The question of whether or not presidential debates actually matter has irked political scientists and pundits for some time, but this might be the year they finally get some answers.
Vox’s Andrew Prokop has a good summary of the existing literature on the issue. Looking at polling data and research by political scientists Prokop writes,
[W]e haven’t seen major poll changes that are attributable to the debates. But that doesn’t mean we’ve seen no change. … [I]t’s actually quite common for polls to shift by two to three points during debate season. … It’s probably not always the debates themselves that are moving polls here. Many other things happen between the start of debate season and the end. For instance, Barack Obama’s bump of 3 points or so during the 2008 debate season may have owed more to the unfolding economic crisis than his debate performances.
This is the general consensus among people attempting to measure the effectiveness of debates on electoral outcomes. It’s unlikely that any debate in the modern era has had a dramatic enough effect on public opinion to sway the outcome of an election.
Only in cases where the electoral margin was razor thin can debates be said to even potentially have changed who won the race. This may have been the case in 2000, in the race between George W. Bush and Al Gore. It was one of the closest elections in American history, where 1 to 2 points could have made all the difference.
But even in this storied example it’s hard to determine the effect of a national debate when the margins were so close that any one event could have swayed the election. Plus, Gore actually won the popular vote. So it's even harder to quantify the diffuse effects of a nationally broadcast debate on an election that was ultimately decided by a handful of Floridians and the U.S. Supreme Court.
Given all that, one might expect that the effect of debates on the 2016 election will be equally marginal and difficult to measure.
But, just like everything else in 2016, this year is different. This year’s presidential election could be the first chance we get to see how much a presidential debate can actually change the outcome of an election. That’s because this year, a bajillion people say that they are going to watch this debate.
One advertising expert interviewed by Ad Week estimated that as many as 80 million people will tune into the live broadcast on Monday night to watch Hillary Clinton and Donald Trump’s first head-to-head matchup. A poll by the Morning Consult found that as many as 106 million registered voters plan to watch the debate on television.
For context, the previous record for the most watched debate was in 1980 when 80 million viewers watched Jimmy Carter and Ronald Reagan duke it out on live television. It’s worth noting here that in 1980 that number likely comprised almost the entire audience for that debate.
This year, the presence of online streaming, DVRs and non-contemporaneous web video will allow millions more people to be view the debate both during and after it’s broadcast.
If the debate really does draw an audience of that historic size it’s easy to imagine that any marginal effect it would otherwise have on the electorate could be amplified. And that could create, not only a unique moment in presidential debate history, but also a chance to finally see if debates between candidates at the apex of their viewing potential can change the course of history.