Incumbent presidents have a substantial advantage for reelection. Only 10 have lost. Statistical models that attempt to control for other factors, such as the economy, typically give a presidential candidate a bonus of 4-8 percentage points just for being the incumbent. In 2009, David Mayhew noted that parties had won the White House only half the time when they didn’t run an incumbent for reelection, but two thirds of the time when they did. That disparity is a little smaller now that Trump has lost a reelection race, but it’s still substantial.

Incumbents also have a vast advantage in their own party’s nomination race, with only Franklin Pierce actually losing his party’s support while he was in the White House. (Several others have chosen not to run.)

However, it’s not clear what these patterns mean for 2024. After all, two leading candidates have recently been presidents of the United States. Whether one, both, or neither will get an incumbency advantage is hard to tell from the historical data. There have only been 59 presidential elections ever, and only 23 in the modern era since FDR beat Hoover. Many variables are relevant to the outcomes of these cases. It is therefore hard to detect which aspects of incumbency may matter–and certainly hard to extrapolate any patterns to our unprecedented situation.

(I think that only one president was unseated but got his original party’s nomination again in a subsequent year: that was Grover Cleveland, who won the rematch.)

Mayhew identified 12 possible explanations for the presidential incumbency advantage and collected the evidence that might bear on each explanation. See his table 3.

Some of these factors presume that the incumbent typically has impressive “capabilities,” because a president has already managed to win a national election and has governed for up to four years. The challenger could be equally capable, but the odds are against it.

In this case, I personally think that Joe Biden has demonstrated strong capabilities, whereas Trump’s campaigns and his time in office demonstrate a blatant lack thereof. However, it doesn’t matter what I think, but what the electorate decides. According to today’s New York Times/Siena poll, 44 percent of Americans agree with me–they hold a very unfavorable view of Trump–but 42 percent strongly disapprove of Biden’s performance in office. What is unusual is the fact that both likely nominees have recently served as the president, which may make this factor a wash.

Voters might also simply prefer a candidate who already holds office. For instance, perhaps some voters are risk-averse: biased against changing horses. Or perhaps they think that any newcomer would need too much time to become effective. Risk-aversion might help Biden a bit in 2024, although some voters may feel that electing him in 2020 was the unwise change. Voters can presumably see either Trump or Biden as the status quo if they want to. Some Trump voters even believe that he is the rightful winner of the most recent election.

“Incumbent party fatigue” refers to the pattern that each party loses a small amount of support–on average–each year that it holds the White House. However, this trend does not doom incumbents, in part because too little “fatigue” typically occurs within four years. The candidates who tend to suffer are those who try to succeed a president of the same party.

The explanations that Mayhew calls “strategic behavior” are of the following type. Perhaps the party of an incumbent president typically organizes to renominate him if he’s been doing well but moves against him if not–as was the case with LBJ in 1968. That would imply that incumbents who run for reelection have generally had successful first terms. And perhaps the opposition party is easily captured by marginal figures when its prospects already look weak against a popular incumbent (consider Barry Goldwater in 1964, or Michael Foot against Margaret Thatcher in 1983). However, Mayhew does not see a lot of power in this type of explanation.

Somewhat buried in his list are factors under the incumbent president’s direct control, such as the ability to allocate funds (e.g., to decide whether to locate the Space Command in Colorado or Alabama), where to deploy cabinet members, which bills to sign or veto, etc. Early in 2021, I predicted that the “$1.9 trillion American Rescue Plan Act of 2021 would prove popular by putting cash directly and quickly into people’s pockets,” and this would help Democrats in 2022. Democrats did somewhat better than most people expected that year, but there’s no evidence that nearly $2 trillion helped them electorally. (In other words, I was wrong.) The other side of the coin is that presidents must make difficult and unpopular decisions.

Overall, I think that Biden has an advantage in 2024 if the economy avoids a deep recession. I think a substantial Biden victory is possible if the economy starts to lift. I suspect that the 4-8 point incumbency advantage–which would typically give Biden a landslide–will not apply, because the electorate will split on the question of who is the rightful incumbent in the first place.

*Mayhew, David R. “Incumbency Advantage in U.S. Presidential Elections: The Historical Record.” Political Science Quarterly, vol. 123, no. 2, 2008, pp. 201–28. See also: 1984 all over again? The Reagan/Biden analogy; What kind of a claim is “Biden has an 87% chance of winning”? (on the metaphysics of probability)