Skip to main content
ABC News
What We Know About The Impact Of Primary Debates

The first Democratic primary debate is almost here. We’ve heard a lot about the rules for who makes the stage, but will these debates actually affect how Democratic primary voters make their decision who to vote for, or how they evaluate the candidates?

Political science tends to be skeptical of general election debates. The people who are most likely to tune into debates tend to be highly informed and already engaged in politics — and thus already likely to have formed an opinion. This has become especially true in recent years as partisanship has grown stronger.

Nevertheless, there is evidence that debates can still affect voters’ impressions of candidates, especially in primaries. It’s all about the context in which a debate is taking place. And we happen to be at a point in the 2020 cycle when debates tend to be most effective.

Here’s a look at what political science has told us about debates over the years and what that could mean for 2020.

Debates help voters evaluate candidates, and can change minds — under the right circumstances

A debate’s main purpose is to help voters decide which candidate they want to support. And there is evidence that primary debates can change people’s minds. Research by University of Missouri communication professors Mitchell McKinney and Benjamin Warner found that nearly 60 percent of study participants experienced a shift in their candidate choices after watching a debate.

But the circumstances matter. First, debates are more important in primaries, as voters can’t rely on their party identification in selecting a candidate. While vote choices in general elections are mostly shaped by partisanship — and thus debates have a limited effect — primary voters are looking for other differences, such as whether candidates are likable, electable or compatible with them on issues. Studies show that debates affect these perceptions.

Generally, the academic research also agrees that debates have the most impact when voters have relatively little information about the candidates and it’s still early in the election cycle (that is, where we are now).

Debates are also most useful when the field is crowded (again, like now) because they can help lesser-known candidates appear electable. One study from the 1996 Republican primary found, for example, that watching the primary debates had a substantial effect on candidates’ perceived viability. In that study, debate viewers rated businessman Steve Forbes’s chances of winning the nomination and beating Bill Clinton in the general election more highly after the debate. By contrast, the debate hurt former Education Secretary Lamar Alexander’s perceived electability.1

But those potential effects are limited — particularly by the rules and structure of the debate. A study of the 2012 Republican primary debates noted that candidates who were already doing well in early polls were afforded more speaking time; so, depending on the format, debates might not actually do that much to boost minor candidates.

How debates are covered in the media also matters

Debates don’t just affect those who watch them; they can also influence the political environment by how they are covered in the media. Candidates don’t have the final say on how their debate performances are portrayed, but that portrayal matters: not everyone will watch the debate, but there’s evidence that voters are responsive to how the media reports on the candidates’ performances. For instance, a study from the 2004 general election found that media coverage immediately following the 2004 general-election debates favored then-President George W. Bush over then-Sen. John Kerry, and that that coverage “persuaded potential voters to alter their attitudes regarding the competing candidates.” Voters were more likely to have a favorable opinion of Bush after the post-debate spin and analysis.

Which naturally raises a question: How do news media outlets decide who “won” a debate, or how to portray what happened? Well, that’s not really clear. But it’s not exactly a perfect reflection of what the candidates say. Researchers found that news coverage of both the Republican and Democratic primary debates in 2000 focused more on sniping between the candidates than on the candidates’ positions.2 Instead of engaging with the candidates’ statements on issues such as homeland security or healthcare, news analyses focused on campaign strategy and election chances.

Additionally, some candidates may receive a more favorable portrayal based on factors outside their control. In the 2020 cycle, the media has already faced criticism for portraying male candidates differently from female candidates, and for emphasizing ill-defined characteristics such as likability over policy ideas.

What this means for 2020

As we’ve discussed, primary debates are a way for voters to evaluate candidates — with, that is, the media also playing a big role in how they are perceived. Something to watch in the 2020 Democratic primary debates is whether candidates hovering around 1 percent in the polls will be able to garner more support, or if the field will winnow as momentum builds around a few front-runners.

How minor candidates do is particularly relevant for 2020 because the field is so crowded. While most of the strongest candidates — based on their current polling averages — will be in Thursday’s debate, the first night will feature Sen. Elizabeth Warren alongside a few candidates who have struggled to hit more than 2 percent in the polls and six more who barely cracked 1 percent. The research is inconclusive as to whether being the front-runner is a built-in advantage in a debate. It’s possible that being the polling leader — at least, on that night’s debate stage — may give Warren an advantage, such as by earning her additional speaking time. Or, a more level playing field might be an opportunity for someone like Beto O’Rourke or Amy Klobuchar to have a breakout moment.

The other 2020-relevant lesson from the research: A breakout moment is more likely to happen if the news media agrees that it happened. (If a tree falls in the forest … .) If Kamala Harris or Warren — who have both hovered around third place in the polls — were to be crowned the “winner” of a primary debate, it could shake up the race and threaten Joe Biden and Bernie Sanders’s polling leads. If the post-debate media narrative is more muddled, we’re less likely to see a big shift in the race.

Finally, beyond the horse-race, the debates might serve simply to add to the interest in the presidential primary, drawing voters into the process — as research has shown debates can. If the high turnout in the 2018 midterms is any indicator, political engagement is high right now. It’s also possible that the debates will help to focus the discussion, highlighting critical differences in beliefs, policies and approaches among candidates.

Or, we may just end up talking about Pete Buttigieg answering a question in Norwegian. Stay tuned.

Here’s what FiveThirtyEight is watching for during the debates


  1. Front-runner (and eventual nominee) Bob Dole also lost some points with debate viewers by not participating in the debate at all.

  2. Looking at the 2004 election, scholars also found that media emphasis on the horse-race aspect of debates — who won, rather than the issues raised — can detract from the substance that these events might otherwise provide.

Julia Azari is an associate professor of political science at Marquette University. Her research interests include the American presidency, political parties and political rhetoric. She is the author of “Delivering the People’s Message: The Changing Politics of the Presidential Mandate.”