The first presidential debate landed with an unpleasant thud. A CBS-YouGov poll found that 83 percent of voters who watched the faceoff found the tone negative, and moderator Chris Wallace expressed regret that it had descended into such a circus — largely because of President Trump’s nonstop interruptions and hectoring of former vice president Joe Biden.

Trump and Biden — but Trump in particular — focused on the failings and shortcomings of the other candidate rather than making a positive case for themselves. In short, the debate was the equivalent of one very long negative advertisement. What kind of effect is such a grim tone likely to have on the race, especially as harsh incivility comes to suffuse not just the debate but the entire campaign? The research suggests that it will turn off independent and moderate voters and further polarize an already deeply divided electorate.

A whole season of negative campaigning is likely to help Biden more than Trump, since the Democratic candidate has a larger base by now. But it will come at a cost, further poisoning the American political environment.

We helped begin a fresh wave of research on negative campaigning and its effects on political engagement in the early 1990s, with a series of studies of, and experiments involving, actual political advertising. While some of the specific findings vary, the body of scholarly work largely agrees on two ways that negativity corrodes our political system.  

First, it drives voters, especially independents and moderates who are not strongly committed to either party, away from politics altogether. Negative political speech tells undecided and nonpartisan voters why they shouldn’t like the candidate who is attacked, yet they also come away with a less favorable opinion of the candidate doing the attacking. So unattached voters wind up with even more reason not to engage with politics. And when they tune out, our system becomes less democratic. (In the 2016 American National Election Studies, the proportion of unaffiliated Americans — independents who lean toward neither party — was around 15 percent.)

Of course, these independent and moderate voters who get turned off by negativity are pretty much by definition less dogmatic in their views than people committed to a candidate or a party. That dynamic helps to explain a second way that negative political speech weakens our political system.

As more nonpartisans become alienated by political speech, the two parties’ bases become even more important to the presidential candidates. And a large body of research has shown that negative political speech energizes a candidate’s supporters in a particular way: It increases the degree to which partisans dislike the opposing party — a phenomenon political scientists call affective polarization.

One of the most distinguishing features of partisanship today, as opposed to 50 years ago, is that it is driven much more by negative feelings about the other party than by positive feelings about one’s own party. The partisan aversion spills over into all aspects of life. Surveys show that between a third and half of partisans express reservations about the prospect of their children marrying into the opposing party, for instance.

To be sure, there is nothing new about negativity in American politics. The 250-year history of U.S. democracy is replete with slanderous news stories, ugly attacks and rough debate tactics. But by every measure that we and other scholars have examined, negativity has grown steadily over a significant period of time — at least the past 50 years. Close examination of the radio, television and film ads in an ample collection at the University of Oklahoma, for example, reveals that political communication has become increasingly about the opponent’s weaknesses and failings.

The news media bears some responsibility for this trend. Bad news is always more newsworthy than good news, giving candidates a significant incentive to go on the attack. The immediate media coverage of the first Trump-Biden showdown ignored the substance of the debate — and yes, there was discussion of health care, the pandemic, economic recovery, racial inequality and climate change — to instead fixate on the tone the candidates set (and on the shell-shocked reaction of viewers, especially undecided ones). That was part of the story, of course, but it wasn’t the whole story.

Belatedly, the Commission on Presidential Debates is considering restructuring the next two meetings to avoid a repeat performance. Many people have said it would be productive if the moderator could cut off a candidate’s mic. Sadly, we think it’s highly likely that the next two debates — assuming they occur — will feature more of the same biliousness, and there is social science research to back that up.

Faced with negative attacks, candidates feel compelled to use a tit-for-tat strategy, which can spiral out of control. In one study, for example, when we showed people competing 30-second political television ads, their response when one candidate was in attack mode and the other stayed positive was to favor the aggressive candidate. (The sample included attacks both on policy — on issues including crime and unemployment — and personal competence.) Candidates sense this intuitively, so when they are attacked, they go on the attack themselves. The need to avoid appearing weak is very real. That helps explain why Biden, who tried at first to remain aloof from Trump’s salvos, ended up calling him a “clown.” That primal psychological response of partisans to a perceived in-group threat makes it almost inevitable that the next presidential debate will pick up where the first one left off.  

Stricter control over the format might help around the margins. For too long, the debate commission has caved to the demands of the campaigns, and it should assert its independence. A mute button could enforce a modicum of civility, as might awarding additional time to a candidate who is interrupted. But given that negativity feeds on itself, our best advice is to buckle up: It’s going to be a rough ride to Nov. 3.