TL;DR
The conventional wisdom often assumes that high turnout benefits Democrats. However, conventional wisdom does not always hold. In general, research has found that it is often not predictive which party will benefit from higher turnout. This is since turnout is often complicated by various factors, such as the group (ethnic, education level, etc.) with higher turnout and also the state at hand.
Insightful articles
Long read
The conventional wisdom assumes that high turnout often benefits Democrats, mainly due to the following reasons:
First, the percentage of registered voters in Democratic-leaning groups—African-Americans, Hispanics, low-income voters, and single people—is lower than among Republican constituencies.
Second, Democrats have a better record of getting their voters to the polls on Election Day. Early indicators suggesting that voters will turn out in droves on Election Day “must be giving Karl Rove heartburn,” McDonald said.
Source: Event Summary: Voter Mobilization and Turnout, Brookings Institution
FiveThirtyEight also ran an article noting some reasons that high turnout benefits Democrats.
“Conventional wisdom has been that if all nonvoters turned up to vote there would be an overwhelming win for the Democratic Party,” said Evette Alexander, a director at the Knight Foundation who participated in the survey design.
[ ... ]
Here are some insights into who these nonvoters are:
- Nonvoters are less white, less educated, poorer, younger and more likely to be women than those who do vote.
- Nonvoters lean slightly Democratic overall, but they favor President Trump in some key states.
- It’s possible that some of these nonvoters will vote in 2020.
- Many nonvoters say the main reason they don’t vote is because they feel disengaged.
Source: Increased Voter Turnout Could Benefit Republicans Or Democrats In 2020, FiveThirtyEight
However, such conventional wisdom is often not decisively seen in elections.
The narrative arising from the 2020 presidential election appears to disagree with the claim that high turnout favours Democrats more than Republicans.
This election debunked a story Democrats had told themselves for decades: that when more voters turn out, they win. When they saw turnout spiking, even in Republican-friendly areas, they assumed that the low-propensity voters heading to the polls were theirs.
[ ... ]
The vote broke that way in state after state, with both parties hitting or exceeding their “win numbers” — the raw total estimated to deliver a win, no matter what the other party pulled off.
Source: The Trailer: Democrats won the White House and lost a myth about turnout, The Washington Post
The Upshot from The New York Times ran an article analysing which party benefits from higher turnout, concluding that it largely depends on the state and the group of voters that turnouts.
Even if every single citizen were to turn out, the effect on the presidential race would not be clear. The president’s approval rating would probably sink by around a point, compared with the 2018 electorate. But the effect on individual states could vary widely.
The major Democratic advantage among nonvoters, their ethnic diversity, would do little for Democrats in the Midwest, where the population is more white and where nonvoters are likelier to be working-class whites who appear to view the president relatively favorably. Democrats would gain more in the diverse but often less competitive states.
[ ... ]
Higher turnout could even help the president [in the crucial Midwestern battlegrounds], where an outsize number of white working-class voters who back the president stayed home in 2018, potentially creating a larger split between the national vote and the Electoral College in 2020 than in 2016.
Source: Which Party Would Benefit Most From Voting by Mail? It’s Complicated, The New York Times
(emphasis mine)
Furthermore, research has shown that turnout rates are not predictive of any party.
The voting eligible population turnout rates don’t show a clear pattern either in past presidential elections. Here are the lists of Democratic and Republican presidential wins and the voting eligible turnout rates back to 1972. (The data go back to 1789 on the United States Elections Project website, run by Michael P. McDonald, a political science professor at the University of Florida.)
Source: Sanders’ Shaky Turnout Claim, FactCheck.org
(emphasis mine)
Research has also shown that turnout can only affect elections that are really close, with the youth vote used as an example in this particular research.
A much smaller percentage of the youth vote in midterm elections than vote in presidential elections, McDonald wrote, so if they did turnout for the midterms in the same numbers, that could make a difference for Democrats. But only in razor-thin races: McDonald found Democratic candidates would have garnered an additional 1 percentage point of the vote in the 2010 midterms if the electorate had been like that of the 2008 presidential election.
Sides and his colleagues aren’t the only researchers to have reached the conclusion that full turnout would alter very few election outcomes. For instance, Sides cites the work of Thomas L. Brunell of the University of Texas at Dallas and John Dinardo of the University of Michigan. Their November 2004 paper on the simulated outcome of full turnout in the 1952 through 2000 presidential elections concluded: “Higher turnout in the form of compulsory voting would not radically change the partisan distribution of the vote.”
Source: Sanders’ Shaky Turnout Claim, FactCheck.org
(emphasis mine)
