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When I reached the longtime Democratic strategist James Carville via text near the end of last nights presidential debate, his despair virtually radiated through my phone.

I tried, man, I tried, Carville wrote to me.

A few minutes later, when the debate was over, we talked by phone. Carville has been one of the loudest and most persistent Democrats arguing that President Joe Biden was too old to run again. Carville, who managed Bill Clintons 1992 presidential campaign and is still, at 79, an influential political analyst, had tempered that criticism latelythough more out of resignation than conviction. His apprehension about Bidens ability to beat Donald Trump had never really diminished in my previous conversations with him, but hed seemed to accept as inevitable that the party would not reject a president who wanted to seek a second term.

But last night, Carville, like other Democrats I spoke with, sounded almost shell-shocked, as he searched for words to describe Bidens scattered, disoriented, and disjointed debate performance.

What is there to fucking say? Carville told me. How could somebody not see this coming? Im just flummoxed.

What do you think will happen next? I asked. I have become aware of the limits of my own power, Carville responded. He thought that Biden running again was a terrible idea. I said it publicly. I failed I understand that. But how could you not see this coming?

I had one last question. What do you think should happen nextshould Biden step aside? I dont know, he said, in a leaden tone. The Democratic Party is at a come-to-Jesus moment. Thats where we are.

Read: A disaster for Joe Biden

Carville was far from the only Democrat reconsidering a scenario that had seemingly passed into political fantasy: whether Biden could be persuaded, or pushed, not to run again. Another prominent Democratic strategist, who is considered one of Bidens staunchest defenders in the party and did not want to be named for this report, told me his view last night that theres a very high likelihood that hes not going to be the candidate. Even so, the strategist added, I dont know how that happens.

If Biden insists on staying in the race, the odds remain high that Democrats will in fact nominate him at their convention in August; dislodging an incumbent president is a huge task. But more Democrats in the next few days are likely to crack open the party-nomination rules. And those rules actually provide a straightforward road map to replace Biden at the convention if he voluntarily withdrawsand even, if he doesnt, a pathway to challenge him.

Trump was hardly a colossus in the debate. Though less belligerent than in his first 2020 debate with Biden, and far more vigorous than Biden last night, Trump continued to display all of his familiar negative traits: He lied almost obsessively, defended the January 6 rioters, bragged about his role in overturning the constitutional right to abortion, and repeated his discredited claims that the 2020 election was stolen from him.

Nothing in Trumps performance convinced Democrats that he could not be beaten in November. But Trumps evident vulnerabilities will probably compound the concern about Biden, because they showed that Democrats might still stop him if they had a candidate who was not laboring under so many painfully apparent vulnerabilities of his own.

For Democrats fearful that Biden cant win, the presidents showing last night was so bad that it might have been goodin the sense that it put the idea of replacing him as the nominee, which the White House had almost completely banished from conversation, back on the table. The pro-Biden strategist last night flatly predicted, I do think that somebody is going to declare and challenge him.

Read: Dropping out is Bidens most patriotic option

Some top party strategists said last night that they considered the widespread panic over Bidens performance a hysterical overreaction. Missed opportunity, but the idea that it is a game changer is totally wrong, Geoff Garin, the experienced Democratic pollster, told me.

Jenifer Fernandez Ancona, a co-founder of Way to Win, a liberal group that focuses on electing candidates of color, offered no praise for Bidens performance but also did not view it as an insurmountable obstacle to beating Trump. This election has always been bigger than these two candidates and their performances, she told me. The choice and contrast between the two different futures they represent is clear and will become more stark as we get closer to Election Day.

But these voices were very much the exceptions in the communal cry of despair that erupted from prominent Democrats last night. Unmitigated disaster was the summary of one, who is a senior strategist for an elected Democrat considered a possible Biden replacement and who asked to remain anonymous. I think there was a sense of shock at how he came out at the beginning of this debate, how his voice sounded; he seemed a little disoriented, David Axelrod, the chief political strategist for Barack Obama, said on CNN immediately after the debate. He did get stronger as the debate went on, but by that time, I think the panic had set in.

The key mechanism in the party rules that allows for replacing the nominee resulted from a change approved decades ago after the bitter 1980 primary fight, when Senator Ted Kennedy of Massachusetts challenged a weakened President Jimmy Carter for the nomination. After a convention battle, which Carter won, Democrats agreed to eliminate the so-called robot rule, which required convention delegates to vote on the first ballot, at least, for the candidate they were chosen to support, says Elaine Kamarck, a senior fellow in governance studies at the Brookings Institution, who played a central role in the change.

Instead, she told me last night, the rules now say that delegates to the convention shall in all good conscience vote for the person they were elected to represent. This means, she added, that there is a presumption you will vote for Biden, but the all good conscience could cover a lot of things.

If Biden voluntarily withdrew, the party would employ a process to replace him that harks back to the era when presidential nominees were selected mainly not through primaries but by party leaders at the convention itself. If he does it himself, there are many, many ways to replace him, Kamarck told me. About 4,000 people have already been elected to the convention. If Biden stepped aside tomorrow, several people would get into the race, no doubt, and the race would consist of calling these people and trying to convince them.

It would be an old-fashioned convention, she went on. All 4,000 delegates pledged to Biden would suddenly be uncommitted, and youd have a miniature campaign. Under changes approved after the Hillary ClintonBernie Sanders 2016 race, the so-called superdelegatesabout 750 elected officials and other party insiderswould become eligible to vote only if no candidate won a majority on the first ballot and the race went to a second round at the convention.

If Biden remains in the race, another candidate could still make a case to the convention delegates for replacing him. Even after last nights performance, though, Kamarck doubts that a serious party leader would try this. I dont think anybody will challenge him, frankly, she told me. I think the depth of feeling for him in the party is very strong.

But the staunchly pro-Biden strategist who expects a challenge thinks the operation could play out in a way similar to the two-step process that helped persuade Lyndon B. Johnson, the previous Democratic president not to seek reelection, to step aside in 1968. Johnson that year initially faced an antiVietnam War challenge from Senator Eugene McCarthy of Minnesota. After McCarthya relatively peripheral figure in the partyshowed Johnsons weakness in the New Hampshire primary vote, Senator Robert F. Kennedy of New York, amuch more formidable opponent, jumped in. Fifteen days later, Johnson announced his withdrawal from the race.

If a challenge to Biden develops before the August convention, the strategist predicted, it would unfold in a similar way. First out of the box will be a secondary figure unlikely to win the nomination, the strategist said. But if that person demonstrated a sufficient groundswell of desire for an alternative candidate, more heavyweight contenderssuch as Governors Gretchen Whitmer of Michigan and Gavin Newsom of Californiamight quickly follow, the strategist predicted.

Talk of replacing Biden may conceivably dissipate once the initial shock of last nights debate fades. Most Democrats who want to replace Biden also remain extremely dubious that his incumbent running mate, Kamala Harris, could beat Trumpbut if she sought the nomination, then denying that prize to the first woman of color who has served as vice president could tear apart the party. The fear that such a fight could practically ensure defeat in November is one reason Democrats who are uneasy about renominating Biden have held their tongue for so long.

Read: Time to go, Joe

Still, the prospect of the party simply marching forward with Biden as if nothing happened last night seems difficult to imagine. Even before his disastrous performance, Democratic anxiety was rising with the release of a flurry of unsettling polls for Biden in the 48 hours before the CNN debate. National Quinnipiac University and New York Times/Siena College polls released Wednesday each gave Trump a four-percentage-point lead over the president, the challengers best showing in weeks. Yesterday, Gallup released a withering national poll that showed the share of Americans with a favorable view of Trump rising, while Bidens number was fallingwith more respondents saying that Trump, rather than Biden, had the personal and leadership qualities a president should have.

Tellingly, three-quarters of those whom Gallup polled said they were concerned that Biden is too old to be president, exactly double the share that registered the same concern about Trump. Like the Times/Siena and Quinnipiac polls, Gallup also found that Bidens job-approval rating remained marooned below 40 percenta level that, as Gallup pointedly noted, is much closer to the historical results at this point in the race for the recent incumbents who lost their reelection bids (Carter in 1980, George H. W. Bush in 1992, and Trump in 2020) than those who won a second term.

Not all the polling on the debates eve was as glum for Biden. But the overall picture suggested that whatever polling boost Biden had received from Trumps criminal conviction in the New York hush-money case a month ago has evaporated. Instead, polls are showing that the former president has regained a narrow but persistent advantage, both nationally and in the decisive battleground states.

All the usual caveats to ironclad conclusions from last nights set piece apply, even if it was a debacle for Biden. Presidential races are marathons, with unpredictable twists. Many Democrats still believe that Biden is a decent man who has been an effective president. The resistance to Trump remains deep and durable among large swaths of the American electorate.

But the viability of Biden as the candidate who can overcome Trumps lead looked much more doubtful within moments of the president taking the stage last night. Bidens performance justified every fear of the cadre of longtime party strategists, such as Carville and Axelrod, who have openly voiced the concerns about renominating him that plenty of others have shared only privately.

Carville, though, was feeling no told you so joy last night. His parting words to me: I hate being right.