A comatose Joe Biden would make a better president than Donald Trump. And the president’s capacity to lead the executive branch is, by most accounts, far greater than his capacity to speak in coherent, extemporaneous sentences on CNN.

But the idea that Joe Biden is the best possible standard-bearer for the Democratic Party this November has lost all plausibility.

At the first presidential debate in Atlanta Thursday night, Trump spouted an endless stream of deranged lies, painting a portrait of a nonexistent United States in which babies are summarily executed in maternity wards, undocumented criminals live in the penthouses of luxury hotels on Uncle Sam’s dime, and the world’s wealthiest nation has become “a Third World country.”

But Biden’s senescence spoke louder than Trump’s mendacity.

The president spoke in broken sentences through a soft, sometimes tremulous voice (Biden’s campaign said that he had a cold). At various points, his mind failed to keep pace with his lips, causing him to abandon a half-delivered talking point or else lose his train of thought entirely. In one excruciating early moment — while trying to advertise his administration’s efforts to cap the prices of prescription drugs for Medicare beneficiaries — Biden said that he had been “making sure that we’re able to make every single solitary person eligible for what I’ve been able to do with … the Covid … excuse me, with, um, dealing with everything we have to do with … uh … look … if … we finally beat Medicare.”

The president’s visual appearance was similarly unsettling, his skin pallid and his mouth hanging oddly agape during some of Trump’s answers.

This despairing spectacle — of a viciously dishonest insurrectionist turning in a debate performance that, if juxtaposed with anything but the president’s even more disjointed efforts would have seemed astoundingly rambling and incoherent — led many Democrats on social media and in private channels to call for Biden’s replacement.

Those calls are now irrefutable.

Americans currently disapprove of the president’s job performance by a roughly 18-point margin, according to FiveThirtyEight’s polling average. By contrast, voters disapprove of Trump by only 11 points on average, and Kamala Harris by only 10.

When asked whether they plan to vote for a Democrat or Republican for Congress, voters favor Democrats by a margin of 45.6 to 45.1. In polls of battleground state electorates, Democratic Senate candidates routinely run far ahead of Biden. Democrats have plenty of political challenges as a party, but Biden had even more as a candidate even before the cameras started rolling in Atlanta.

The president is saddled with the misfortune of presiding over the highest inflation in four decades. This does not reflect any great economic mismanagement on his part; to the contrary, he has shepherded the US to the strongest recovery of any G-7 country. Yet, across the wealthy world, more or less every leader who presided over 2022’s inflation has suffered overwhelming public disapproval. For many voters, Biden is the personification of price increases. Even if he were in his prime as an orator, there would be a case for swapping him out merely because bad luck had damaged his brand.

But of course, Biden is not in his prime. He would be 82 years old at his second inauguration and 86 at the close of his second term. It strains credulity to claim that the person best suited to run the United States is an octogenarian. Were the Democratic nominee anyone else, Trump’s age — 78 — would be a significant liability for the Republicans. But Biden is three years older than Trump, andseems about a decade his senior.

Or so voters appear to think. In an ABC News poll from February, 86 percent of voters said that Biden was too old to serve another term.

Partly for these reasons, Biden has been trailing Trump in polls of virtually every swing state. And in both 2016 and 2020, the polls significantly overestimated Democratic support in the Electoral College’s battlegrounds. Before Thursday night, Nate Silver’s model gave Trump a 66 percent chance of winning.

Thus, there was already a solid case for Biden to step aside and let Kamala Harris or some other Democrat lead the party into November’s election, even before his dispiriting debate performance. By far the most likely consequence of staying the course was America’s reelection of a corrupt and authoritarian reactionary. Rolling the dice on a new candidate was plausibly the party’s best move.

Then, Biden went on national television and made it impossible for anyone to honestly say, “I am confident that the president will still be fit to serve in January 2029.”

There is no way for the Democratic Party to deny Biden the nomination at this point. But Democratic leaders could personally lobby the president to step aside and endorse his preferred successor, preempting the hazards of a contested Democratic convention in late August. Waiting months to anoint a presumptive nominee would be highly risky. Rallying around Biden’s handpicked heir now would be much less so.

If one wishes to minimize intra-party strife, then Biden could simply endorse his vice president, who already functions as his default replacement. Few consider Harris to be among her party’s best political talents, but she offers far more upside than the version of Biden we saw Thursday night.

If Democratic leaders believe that it would be possible for Biden to endorse a more electorally formidable candidate (perhaps Michigan Gov. Gretchen Whitmer?) without alienating key constituencies, then that might be the optimal course of action. Sticking with Biden, plainly, is not.

The president’s policy positions and governing record matter more than his current skills as a rhetorician. But precisely because of how much is substantively at stake in this election, Democrats cannot afford to wager it on American voters changing their minds and deciding that Biden isn’t too old for his job after watching him struggle to remember the topics of his own sentences.

Many aspects of Biden’s legacy are laudable. His best chance for preserving it would be to voluntarily end his presidency after one term before voters get the chance.