What happens now that Biden dropped out? The chaotic 1968 Democratic convention could be a clue.

The last time a presidential nominee was selected at a Democratic National Convention was in 1968, following RFK's assassination.

• Now that Biden has dropped from the race, it could 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 choosing Vice President Hubert Humphrey.

Democratic President Joe Biden announced Sunday that he is withdrawing from the 2024 presidential race.

For years, Biden has been plagued with critiques about his old age and perceived cognitive skills. That criticism grew exponentially 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.

Criticisms reached a fever pitch in June following a disastrous debate between Biden and former President Donald Trump, which led to weeks of Democratic infighting over whether Biden still had the gusto to beat Trump.

With Biden finally dropping his reelection bid, there's a chance of 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. During late March of that year, 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.

Before Biden's stunning drop from the race, the DNC didn't seem to have much desire to recreate 1968's contested convention in any capacity. Chairman Jaime Harrison said in February 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."

But clearly, time changes minds. Speaking about the potential for Biden to step aside, former Speaker Nancy Pelosi suggested an open nomination process would keep it from appearing as if Democratic leaders anointed Vice President Kamala Harris to the top of the ticket, Politico reported in July.

Shortly after sharing his decision to drop out, Biden endorsed Harris to be the Democratic nominee. While his endorsement certainly helps Harris, it doesn't guarantee her the nomination. Another Democrat could challenge her and try to win the party's more than 4,000 delegates to the Democratic National Convention in August.