The case for Biden 2024 is weaker today than it was immediately after the first presidential debate.

In the wake of President Joe Biden’s disastrous debate performance, Democrats implored their standard-bearer to prove that he had merely “had a bad night”: He could prove his mental acuity, rhetorical competence, and vitality through a blitz of live television appearances and press conferences. And he could demonstrate his cognitive and neurological health by submitting to clinical testing and then releasing the results to the public.

Instead, the president conducted two secretlypre-scripted radio interviews, and then sat for a single, 22-minute television Q&A — after taking a week to prepare — and still repeatedly failed to articulate coherent thoughts. In one of his clearest answers, however, Biden conveyed his adamant refusal to undergo cognitive and neurological testing.

Biden followed this up with a call-in interview to MSNBC’s Morning Joe on Monday. During that appearance, the president seemed to be reading off of written notes — and still sometimes failed to complete his own sentences, trailing off after losing the thread of a talking point about Donald Trump.

Meanwhile, a wide array of Democrats and foreign officials have told reporters that Biden’s debate performance wasn’t an anomaly: The president has repeatedly suffered similarly disquieting mental lapses in private. Democratic donors revealed that Biden bizarrely relied on a teleprompter to deliver remarks in the private home of a patron.

Voters appear similarly unnerved. In multiple polls, upward of 70 percent of Americans say Biden is not fit for a second term. And Trump’s lead over the president has grown both nationally and in battleground states — despite the fact that Biden is drastically outspending his opponent on TV ads, an advantage that will soon disappear as the Republican begins tapping his own formidable campaign funds.

In light of all this, the president’s die-hard supporters have been forced to lean on a variety of unsound arguments for his candidacy. I refuted several of these in a column last week. But a new one gained prominence over the weekend, which can be summarized as, “History teaches us that changing nominees this late in the race is electoral suicide.”

Here is how the Boston College history professor (and hit Substack author) Heather Cox Richardson put the point on CNN Saturday:

In the whole picture of American history, if you change a presidential nominee at this point in the game, the candidate loses. And it loses for a number of reasons. First of all, because the apparatus of the party for the election is set up around somebody else. Second of all, because the news is only going to report all the growing pains of a brand new campaign, including all the opposition research that the opponents are then going to throw at people.

This analysis is badly misguided. It is founded on a fundamentally absurd premise: that we can ascertain eternal truths about politics from the outcomes of exactly two elections. And the argument’s substantive assessment of those elections is also highly dubious. Most critically, though, Richardson completely elides the extraordinary nature of Biden’s liabilities. History cannot tell us what happens when a party chooses to replace its cognitively compromised, 81-year-old nominee because no American political party has ever before faced such a predicament.

The first problem with Richardson’s take is conceptual: You cannot derive timeless laws of political science from a correlation in a dataset with a sample size of two.

In modern US history, a sitting president has abruptly declined to seek renomination in an election year on only two occasions. Harry Truman dropped out in March of 1952 after being upset in the New Hampshire primary. Around the same stage in the 1968 race, Lyndon B. Johnson announced that he would not seek renomination, amid widespread opposition to his handling of the Vietnam War. In both instances, the Democratic Party ultimately lost the general election.

But one cannot draw any general conclusions about the wisdom of switching standard-bearers in an election year from these facts. This is because you cannot responsibly glean any general rule from a correlation supported by two data points. It is true that Donald Trump won a general election when Democrats nominated a candidate under 70 years old in 2016, but then lost when Democrats nominated a candidate over 70 in 2020. But it would be bizarre to look at those facts and conclude that “In the whole picture of American history, when Democrats nominate a non-septuagenarian to take on Donald Trump, the candidate loses.”

Richardson’s reasoning is only a bit less absurd. In 1952, the Democratic Party had held the White House for 20 consecutive years, and the GOP picked a moderate, popular general, Dwight Eisenhower, as its nominee. Is it not possible that Democrats lost for these reasons, rather than because Truman stepped down? For all we know, the party could have done even worse if Truman had been the nominee; we do not have access to the counterfactual. We can’t get in a time machine, change one variable, and then run history again. And without the benefit of such an experiment, we cannot know with certainty whether Truman dropping out helped or hurt his party.

The same can be said of LBJ’s decision to withdraw from the 1968 presidential race. Maybe the Democrats lost that election for the reasons Richardson states: Johnson dropped out, and his replacement, Hubert Humphrey, struggled to win as much support because the “party apparatus” was built around LBJ (whatever that means) and the news media reported on opposition research about Humphrey.

But how precisely are we proving that thesis? How do we establish that Democrats would have done better with Johnson on the ballot? After all, LBJ was even more closely identified with the Vietnam War, and therefore even more likely to internally divide the Democratic coalition, than Humphrey was. And many features of that election cycle favored the Republicans, including a widespread backlash to civil rights and rising crime. Despite these headwinds, Humphrey nearly won the popular vote. How do we know that LBJ wouldn’t have done worse?

Political scientists often compensate for the inherently small sample size of US elections by examining voter behavior abroad. And when we widen the lens, the idea that switching leaders last-minute is always damaging becomes even more dubious. To take one example: In 2017, New Zealand’s Labour Party saw its support fall below 25 percent less than two months before election day. In response, the party’s leader, Andrew Little, stepped down and his deputy, Jacinda Ardern, replaced him. Labour proceeded to gain support, ultimately winning 37 percent of the vote, enough to lead a left-of-center coalition government with Ardern as prime minister.

If Richardson overestimates what we can learn from the past, she also understates Biden’s challenges in the present. His current position is not analogous to that of LBJ or Truman. Both of those men weren’t yet in their 70s, let alone their 80s, as Biden is today. Both also were competent public speakers, and there was no evidence — public or private — that they were suffering from severe cognitive decline.

Richardson’s suggestion that replacing Biden would harm Democrats, as the news media would publish damaging stories about his replacement, is especially odd. If the party sticks with Biden, it is an absolute certainty that there will be news stories spotlighting Democrats’ private concerns about his cognitive health, along with the president’s every public misstep. And it is also certain that Biden will struggle to combat the implications of these stories through vigorous campaigning, and eloquent interviews. We know these things because they are already happening.

By contrast, Richardson’s implicit claim that Biden’s replacement will suffer from more negative media coverage appears to be based on nothing but a hunch. She does not acknowledge that the new nominee would almost certainly be better equipped to both 1) participate in lots of media interviews and 2) speak coherently during them, and might therefore receive more favorable press.

Most critically, Richardson fails to engage with how bleak Biden’s current odds appear. The president has a 37 percent approval rating. He has trailed Trump both nationally and in virtually every swing state for months. Before he advertised his cognitive decline at the first debate, Biden had failed to catch up to Trump despite falling inflation and his rival’s criminal conviction. It is extremely unlikely that the president will be better able to overtake Trump in the coming months than he had been before the depths of his senescence were revealed on national television.

In truth, the question facing the Democratic Party is this: Is running a historically unpopular, 81-year-old president who cannot maintain a normal campaign schedule or speak coherently — and who is considered unfit for leadership by more than 70 percent of voters and many of his own allies in Washington — really the best way for Democrats to keep Trump out of power?

History cannot answer this question, not least because there is no historical precedent for the Democrats’ current predicament.

What we do know is that just about every hypothetical alternative to Biden — Vice President Kamala Harris, Gov. Gretchen Whitmer, Gov. Josh Shapiro, etc. — has a lower disapproval rating than he does. And we also know that making any of those alternate candidates the Democratic nominee would dramatically shake up the presidential race and the narratives around it. Suddenly, the valence of age as an issue would flip: The Democrats would have a nominee in the prime of life, while the GOP would be saddled with a 78-year-old, whose own incoherence and mental lapses would be more apparent against a much younger rival.

This doesn’t mean that a new candidate would definitely perform better than Biden. The fact that fewer voters have a strong opinion about Harris and Whitmer implies that they could win more support than the president — but also, that they theoretically could win less. But at this point, such uncertainty is a virtue. When you are on track for an almost-certain loss, it’s wise to gamble on a course of action with unpredictable consequences. And this is especially true in this specific circumstance, wherein common sense dictates that having a candidate who is physically and cognitively capable of running a vigorous campaign is preferable to having one who looks and sounds irrevocably diminished by age.

To believe otherwise is to mistake historical anecdotes for immutable laws, and status-quo bias for sage insight.