What happens if Biden drops out? The chaotic 1968 Democratic convention could be a clue.

• If Biden drops from the presidential race, it would likely lead to a contested convention in August.
• The last time that happened was in 1968 after President Lyndon B. Johnson quit his reelection bid.
• His late departure from the race led to the party to choosing Vice President Hubert Humphrey.

For years, Democratic President Joe Biden has been plagued with critiques about his old age and perceived cognitive skills. That criticism grew exponentially earlier in February following Special Counsel Robert Hur's report on the president's mishandling of classified documents, which specifically took note of his age and declining memory.

If Biden does take his critics' advice and drop out of the race entirely, the result would most likely lead to a contested Democratic National Convention in August, where delegates previously bound to Biden would have the power to choose November's Democratic presidential nominee.

That scenario hasn't occurred since 1968. In late March, as the US involvement in the war in Vietnam raged on, Democratic President Lyndon B. Johnson announced he would end his reelection bid following a narrow win in New Hampshire's state primary. Less than a week later, a shooter killed civil rights leader Martin Luther King Jr. in Memphis, stoking even more national drama.

Without Johnson, the obvious Democratic nominee, his vice president, Hubert Humphrey, joined the primary fray against Sen. Eugene McCarthy and Sen. Robert F. Kennedy.

Having joined the election cycle late in the game, Humphrey was unable to make it onto several primary ballots. Undeterred, his campaign amassed delegates via an unconventional strategy: having allies stand in for him in certain primaries to disrupt the competition and allow state party leaders to send the delegates his way.

After months of strategic campaigning, in early June, Humphrey had a sizable delegate lead over Kennedy and a several hundred delegate lead ahead of McCarthy. His campaign's strategy appeared to be working, but an unexpected national tragedy quickly complicated its plans: Kennedy was assassinated, upending the primary race.

With no candidate having amassed a majority of the nation's delegates, the Democratic presidential nominee was decided at the 1968 Democratic National Convention in Chicago, where anti-war protesters angrily demonstrated outside.

Tensions were also high inside the convention. Security guards battered news correspondent Dan Rather when he attempted to interview a state delegate, leading fellow broadcaster Walter Cronkite to say, "I think we've got a bunch of thugs here, Dan."

Most of the state delegates at the convention voted for Humphrey, leading him to win the Democratic Party's nomination. He later faced off against then-former Vice President Richard Nixon in November, losing to the Republican Californian by 110 electoral votes.

Following the chaotic 1968 convention election cycle, the Democratic National Committee created a commission to reform the party's method for choosing delegates, leading to a sharp rise in the number of states holding primary elections and the system we still have in place today.

As it stands, it doesn't appear that the DNC has any desire to recreate 1968's contested convention in any capacity. Chairman Jaime Harrison said Monday that the idea of taking the nomination away from Biden and then winning in November — likely against former President Donald Trump — is "certifiably crazy actually."

Unless Biden stuns the party and suddenly drops out, the current 81-year-old president is on a fast track to obtaining the Democratic presidential nomination.