Thursday’s presidential debate debacle — widely regarded as a low point for President Joe Biden, who appeared feeble and sometimes confused — many Democratic elites and nonpartisan pundits are suggesting a break-the-glass-in-case-of-emergency move that resided on the margins of conventional political thought just a week ago: The incumbent president, they argue, should step aside in the interest of the country, and delegates should name his replacement at the upcoming Democratic National Convention.

Any move to replace Biden just four months before the election carries considerable risk. The party can ill afford to pass over its sitting vice president, Kamala Harris, who represents a core Democratic constituency as a Black woman — but Harris consistently underperforms in polling. And allowing delegates to make such a momentous decision, negating the will of millions of primary voters and turning a nomination process that has been the norm for decades upside-down, is surely a recipe for division and rancor.

But it’s not like we haven’t been here before. On March 31, 1968, Lyndon B. Johnson stunned the nation when he announced that he was pulling out of that year’s presidential election. The Democratic National Convention that followed several months later devolved into chaos and violence and left the party’s eventual nominee, Vice President Hubert Humphrey, hobbled at the start of the fall campaign season. He ultimately lost a painfully close election to Richard Nixon, in no small part because of the unruly convention in Chicago.