When I reached the longtime Democratic strategist James Carville via text near the end of last night’s 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 … His apprehension about Biden’s ability to beat Donald Trump had never really diminished in my previous conversations with him, but he’d seemed to accept as inevitable that the party would not reject a president who wanted to seek a second term …

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 withdraws—and even, if he doesn’t, a pathway to challenge him.