After weeks of dismissing criticism and saying he wasn't too old for a potential second term in the White House, Joe Biden announced on Sunday that he would not, in fact, run again. Biden had faced a growing array of voices asking him to withdraw after his poor performance in the first presidential debate with Republican candidate Donald Trump on June 27.

"It has been the greatest honor of my life to serve as your president," Biden said in an online post on Sunday. "And while it has been my intention to seek reelection, I believe it is in the best interest of my party and my country for me to stand down."

That means the Democrats will need to find a new candidate for president ― just under four months before the election on November 5. Here is how that will work.

What would normally happen at the Democratic National Convention? 

Earlier this year, US voters across the country participated in the primaries, the process through which Democrats and Republicans in each state elect who they want to represent their party on November 5. The person who gets the most votes in each state wins that state's delegates. How many delegates each state has depends on the size of its population ― winning in California will get you more delegates than winning in Vermont. 

At the Democratic National Convention in August, the Democrats' delegates will come together and vote for the presidential candidate. In the primaries, Biden won the vast majority of delegates ― some 3,900, with only around 30 staying uncommitted or going to primary candidates who didn't stand a chance. Under Democratic Party statutes, those 3,900 delegates would normally be obligated to vote for Biden.

In recent days, many of those pledged delegates had indicated their support was wavering. To shore up against hemorrhaging too many votes, Biden had been moving to implement a virtual role call to finalize his nomination before the convention.

Now that he has stepped down, all delegates he had initially won are free to vote for whomever they want in what is called an open convention.

What's going to happen at the open convention?

Ahead of the event in Chicago from August 19-22, Democratic leadership will try to find, as quickly as possible, a candidate who they believe can unite the party. The goal is to pick a candidate who will draw voters from across the wide ideological spectrum encompassed by the Democrats to the polls in November. Only if the Democratic candidate can energize enough Americans to get out and vote does the party stand a chance at still beating Trump this late in the game. 

The leadership-approved candidate and their running mate will vie for delegates' votes in Chicago come August, but anyone else can too — that's the idea behind an open convention. If someone believes they would make a better president than the person picked by party leaders, they can try to win over delegates as well. The only thing everyone who wants to run must do is collect the signatures of 600 delegates.

It's important to note that while Biden's vice president, Kamala Harris, is one of the likely picks to be the new presidential candidate, she will not automatically take over from Biden simply because she's his VP. When a president becomes incapacitated while in office, the vice president takes on the job. But the same is not true for becoming the candidate when the president has decided not to run again. 

Back to the convention: There are 3,933 pledged delegates according to Ballotpedia, an online encyclopedia on US politics. They all vote in a first round. If one candidate receives more than 50% of the votes, they will be the new Democratic champion to face their Republican rival in the general election on November 5. 

What is a brokered convention?

If no candidate wins more than 50% of the vote in round one, the event will turn into what's known as a brokered convention. Now Democratic leadership, powerful figures in the party and the potential candidates themselves will talk to the delegates to try to win them over. At this point, new alliances could potentially form, for example when one of the competitors tries to convince a rival to become his running mate instead of running against him.

To get an impression of what this looks like, take a look at US TV shows like "The West Wing" and "House of Cards." Both have episodes portraying the behind-the-scenes drama that goes on at such conventions. In reality, the last time the Democrats had a brokered convention was in 1952.

There will be more voting and now, a group that wasn't allowed to participate in round one gets to vote too: the superdelegates, or unbound delegates.

According to Ballotpedia, there are 739 of them, and as the name suggests, they haven't been pledged to any one candidate through the primaries process. Instead, they are elected members of the Democratic National Committee (the party's leadership), members of Congress, governors and distinguished party leaders. They are never bound to a candidate and, come round two, can vote for whomever they want.

The voting will continue until one candidate manages to secure more than 50% of all delegates' votes, no matter how many rounds it takes. By the end of it, we'll know who will replace Biden as the Democratic candidate for president in the 2024 election.