Presidential hopeful Sen. Kamala Harris Kamala HarrisHarris faces pivotal moment with Supreme Court battle Nearly 40 Democratic senators call for climate change questions in debates Joe Biden has long forgotten North Carolina: Today's visit is too late MORE (D-Calif.) welcomed former Vice President Joe Biden Joe BidenBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Democratic groups using Bloomberg money to launch M in Spanish language ads in Florida Harris faces pivotal moment with Supreme Court battle MORE into the Democratic primary Thursday, calling him a friend and saying he "brings a wealth of knowledge to the race."

“As of this morning, my friend Joe Biden is now running for president. And you know what I say to that? The more, the merrier! Joe brings a wealth of knowledge to the race, and I’m excited to debate ideas and policy with him and the many other candidates running for president in the coming months,” Harris said in an email to supporters.

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The California senator also requested a donation to her campaign, saying she would need funds to help cut through in a crowded primary field that has grown to 21 candidates with Biden’s entry.

“Let me be clear: I intend to win. But with a primary field this crowded, it’s on us to find new ways to cut through the noise and reach more voters. It’s going to take a lot of resources,” she said.

Biden’s campaign announcement, though expected for months, made a splash Thursday, immediately launching the former vice president near the top of the primary pack alongside Sen. Bernie Sanders Bernie SandersOutrage erupts over Breonna Taylor grand jury ruling Dimon: Wealth tax 'almost impossible to do' Grand jury charges no officers in Breonna Taylor death MORE (I-Vt.).

In recognition that Biden’s entry into the race could shake up the Democratic Party’s nominating contests, other presidential hopefuls sent out fundraising requests in the hour’s following Biden’s announcement.

“Joe Biden just announced he’s officially running. The field is the biggest in the history of the modern Democratic Party, and this presidential primary is wide open. Today is an important day to show the strength of our grassroots campaign, especially given the fact that the former vice president has already been collecting checks from major donors for a week leading up to this launch,” former Rep. Beto O’Rourke (D-Texas) wrote in an email to supporters.

“Vice President Biden is officially running. Team — there is no doubt his decision could shake up the race,” wrote Sen. Cory Booker Cory Anthony BookerBipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility MORE (D-N.J.). “More voices make us a stronger party, but even I admit it’s getting hard to keep track of how many Democrats are running for president. As of today, we're at 20 candidates. The truth is this poses a real challenge for an underdog campaign like ours.”

Washington Gov. Jay Inslee Jay Robert InsleeBarr asked prosecutors to explore charging Seattle mayor over protest zone: report Bottom line Oregon senator says Trump's blame on 'forest management' for wildfires is 'just a big and devastating lie' MORE, former Colorado Gov. John Hickenlooper John HickenlooperCook Political Report shifts Colorado Senate race toward Democrat Willie Nelson playing at virtual fundraiser for Hickenlooper Gardner on court vacancy: Country needs to mourn Ginsburg 'before the politics begin' MORE and former San Antonio Mayor Julian Castro Julian CastroSanders says Democrats should have given more speaking time to progressives Castro says DNC should have put more Latino speakers on stage from beginning Jill Biden defends husband's cognitive ability from Trump attacks: 'It's ridiculous' MORE also sent out fundraising requests citing Biden's entry into the presidential race.

Updated at 2:04 p.m.