What happens now that Biden has dropped out and endorsed Kamala Harris

• Biden dropped out the 2024 presidential race and endorsed Vice President Kamala Harris.
• Harris now controls the Biden campaign infrastructure and is quickly locking down support.

Joe Biden announced on Sunday that he would withdrawing from the presidential race.

In a letter released on Sunday, the president said that he believes "it is in the best interest of my party and the country for me to stand down." He plans to complete his term, and will speak more about his decision later this week.

His decision, made after weeks of growing pressure from members of his own party, throws Democrats into uncharted territory. Never before has a major party selected a new nominee so close to a general election.

Biden immediately endorsed Vice President Kamala Harris to succeed him, saying that choosing her as his running mate in 2020 was the "best decision I've made."

Though another Democratic candidate could theoretically mount a challenge, that appears unlikely: a majority of Democrats in both the House and the Senate have already endorsed the vice president, as of Tuesday.

The nominee will almost be Harris — but there could theoretically be an 'open convention'

In many ways, Kamala Harris appears to be the safest option. She's already served as Vice President for three and a half years, is well-known to the public, and — perhaps most crucially — was able to easily take over the infrastructure and financial resources that the Biden campaign had spent months building up.

But some Democrats, skeptical of Harris's chances against former President Donald Trump, had pushed for a "mini-primary" for potential nominees to make their case ahead of an open convention.

Sen. Joe Manchin, an independent from West Virginia who caucuses with Democrats, called for an "open process" to select a new nominee as he called for Biden to step on Sunday. Former President Barack Obama has also endorsed an open process.

Under this scenario, a whole array of potential candidates would have a few short weeks to win over the hearts of the delegates, who would then be free to vote for the candidate of their choice.

There's been a lot of disagreement over this approach. While some believe it could be energizing for the party, others worry it may be divisive. Rep. Alexandria Ocasio-Cortez of New York, a firm supporter of Biden's, has called the idea "crazy."

In any case, it appears unlikely to happen: Every major competitor to Harris had endorsed her by Monday afternoon.

The Democratic National Committee had planned to have a virtual roll call to determine the nominee sometime in early August, ahead of the official convention from from August 19-22 in Chicago, Illinois.

The party's Rules Committee will meet on Wednesday to "implement a framework to select a new nominee, which will be open, transparent, fair and orderly," according to a notice seen by Business Insider.

Republicans will continue hammering Democrats over Biden

One thing is for sure: Even with Biden out of the race, Republicans are likely to use him to hammer Democrats.

After all, he remains the president — and his decision to withdraw also raises fair questions about his ability to serve right now.

Republicans are also likely to accuse Democrats of "covering" for Biden in the months before his disastrous debate performance, a line that many have already taken in the weeks since then.

Democrats who have called for Biden to step aside have often argued that the two questions are separate: They remain confident in his ability to serve out the remainder of his term, but don't believe he can win.

On Sunday, immediately after Biden announced his decision to withdraw, a series of Republican politicians called on Biden to resign immediately, including Speaker Mike Johnson.

"If Joe Biden is not fit to run for President, he is not fit to serve as President," Johnson said. "He must resign the office immediately. November 5 cannot arrive soon enough."

The Kamala Harris veepstakes are now the biggest game in town

With Harris almost certain to be the nominee, the last big remaining question is who her running mate will be.

There are several names floating around, most of whom are governors, including Josh Shapiro of Pennsylvania, Andy Beshear of Kentucky, and Roy Cooper of North Carolina. Sen. Mark Kelly of Arizona is also said to be in the running.

One contender, Gov. Gretchen Whitmer of Michigan, took herself out of the running on Monday.

Meanwhile, Beshear gave what appeared to be a full-throated audition for the job, lacing into Trump's new running mate, Sen. JD Vance of Ohio, in a potential preview of a future vice presidential debate.