Why Kamala Harris is the frontrunner to replace Joe Biden as presidential nominee - as time ticks away for the Democrats

It was 1.46pm in Rehoboth Beach, Delaware, when President Joe Biden posted a letter on his personal account on the social media site X announcing he would be withdrawing from the presidential race.

By 2.13pm he had sent another post, this time endorsing Kamala Harris to replace him as the Democratic Party's nominee.

It took 27 minutes to get there but President Biden has now put his former running mate in the pole position to take on Donald Trump.

There seems limited doubt now that she will be their runner in the race.

Follow live: Reaction as Biden pulls out of race

Mr Biden's original letter had focused more closely on his own achievements as president, investments in affordable healthcare, moves towards gun safety and only a brief mention of Kamala Harris being an "extraordinary partner" in this work.

But any suggestion he wanted to leave the door open for a democratic primary or an open convention was quickly extinguished shortly after, when he offered his backing and "full support" to his vice president.

Soon after, other prominent Democrats lined up behind her.

She now appears to have an uncontested path to the nomination with no other top Democrat announcing plans to enter the race yet.

Logistically, she makes a lot of sense to the Democratic Party.

She already has the Biden/Harris infrastructure around her.

It is also less problematic to transfer the Biden campaign donations - currently a $96m war chest - to her, and Mr Biden could instruct his delegates to switch their votes to Ms Harris.

The prospect of a Harris candidacy also seems to have energised donors. The Democratic fundraising organisation ActBlue said it has raised $46.7m from grassroots supporters in the hours after Ms Harris launched her campaign.

Time is of the essence with just 107 days to go until election day - and a Harris candidacy allows Democrats to get the ball rolling faster and to focus on the ultimate task of defeating Mr Trump.

Ms Harris has already been bashing the phones to Democratic Party donors, leaders in congress and state houses, and over the next few days will be keen to show she is in control of the party.

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There are still so many complications and questions for the Democratic Party to be ironed out if they switch their nomination from Biden to Harris.

Politically, this is uncharted territory, and so is a first woman of colour running for the White House.