Does conflict at the party convention matter?

Should Democrats be concerned about a fight between Bernie Sanders and Hillary Clinton supporters at their party convention in Philadelphia? Should Republicans be worried about protests outside the Quicken Loans Arena?

Maybe.

Some research suggests that prolonged primaries do not harm the eventual nominee, or at least that the results of contested primaries are ambiguous. In addition, there is at least some indication that a competitive primary season, followed by a unifying convention, may actually produce strong autumn results for the party.

On the other hand, some evidence suggests that parties beset by a conflicted convention may underperform in the general election. In an election year characterized by turmoil and uncertainty, these issues are worth consideration.

Party conventions perform two functions in the modern campaign era. First, they serve the official function of nominating the presidential candidates. The outcome of the nomination contests this year is not seriously in doubt — barring an extraordinary turn of events, Donald Trump will be the Republican nominee, and Clinton will be the Democratic nominee.

Even if Sanders “goes all the way to the convention,” Clinton will have the most pledged delegates, the most support from superdelegates, and the most “popular votes.“ Based on those factors, she would almost certainly win the nomination even on a “contested” first ballot. But could such a contest hurt the party?

Party conventions serve a second function in the modern era: They are a three-day advertisement for the party and its ideas. They generate sustained positive news coverage for the party and its nominee. The conventions (perhaps because of that coverage) generate a bounce in the polls that is one of the only durable changes in poll standings during the course of the general election.

A number of factors have been shown to affect the size of the convention bounce. Thomas Holbrook suggests that the convention bounce brings polling into alignment with the fundamentals of the race (which in 2016 would favor the Republicans), and that timing matters as well. The party with the first convention (again, in 2016 the Republicans) often experiences a bigger bounce, but a short time window between conventions (the contests will be separated by four days this year) can diminish the positive effect of going first.

The convention bounce seems to work mostly by reminding leaning partisans why they usually vote for their preferred party and why they should vote for its nominee. A divisive convention risks undermining positive news coverage and the increase in support for the party’s candidate such coverage can produce.

The data we have on convention bounces is noisy, but a number of examples suggest that when a party underperforms its expected convention bounce, the content of the convention, and its news coverage and commentary, may play a role. Divisive conventions and negative coverage do seem to be associated with the most dramatically “underperforming” convention bounces:

Divided parties have sometimes also received larger-than-expected bounces, an effect that may be related to positive narratives emerging from successful attempts to heal party divisions and achieve authentic unity.

Any conclusions about convention effects should be made with all of the appropriate caveats. Partisan divisions that endure into the convention have had inconsistent effects on the state of the race. The number of cases to examine is small. The size of the convention bounce may be totally determined by the fundamentals of the race. The presence of Donald Trump in the race may alter all the rules of politics as we know them.

However, historical examples suggest that party divisions at the convention may be communicated in press coverage, which in turn may affect voters. If conventions affect the polls primarily by generating enthusiasm for the ticket among wavering partisans, the tone of the convention itself could affect those voters’ perceptions.

Examples suggest that a unifying convention that creates a positive media narrative might lead to overperformance in the polls, but they also suggest that a dramatically divisive convention can have lasting and negative impacts. In a year when both parties remain conflicted over their nominees and over policy, it may be difficult to thread the needle between these divergent outcomes. But in a year when the results of the general election are difficult to predict, party leaders should be mindful of that goal.

Casey Dominguez is an associate professor of political science at the University of San Diego. Her research focuses on political parties, campaign finance, and the presidency.

Andrew Tirrell is an assistant professor of political science at the University of San Diego. His research focuses on environmental justice, natural resource management, sustainable development, marine policy, and the Arctic.

This post is part of Mischiefs of Faction, an independent political science blog featuring reflections on the party system. See more Mischiefs of Faction posts here.