Kamala Harris and her allies sprang into action to consolidate support from big donors for her Sunday as President Biden announced his exit from the presidential race.

The vice president and her husband Doug Emhoff held a number of private conversations Sunday with wealthy individuals who have backed her political career in the past. The same day, Harris’s team sent a document to donors and other supporters that said she is ready to “earn and win” the Democratic nomination and she is best positioned to unite the party and beat Donald Trump .

The document, which was reviewed by The Wall Street Journal, cites her experience traveling to more than 20 countries and meeting with more than 150 world leaders, her role as the Democratic Party’s leading messenger on abortion rights, and polls showing her beating Trump and leading the Republican among independents.

“VP Harris is well positioned to mobilize key constituencies of the Democratic coalition, including young voters, Black voters, Latino voters, and women,” the document reads.

The private communications are a signal of how deep Harris’ connection to the donor community runs and how important lining up their support will be to her securing the Democratic Party’s presidential nomination.

Her ties began during the time she spent mingling with San Francisco’s tech community as the city’s district attorney and now extend to Wall Street and entertainment industry moguls in Los Angeles, where she and Emhoff live when not in Washington, D.C.

While other candidates could enter the race, Biden transferred his fundraising committees to Harris on Sunday, and she has already secured support from some of the party’s most moneyed elite.

Within minutes of Biden’s announcement, LinkedIn co-founder Reid Hoffman said he would support Harris for president. Father-and-son pair George and Alex Soros said they also both support her, according to a spokesperson.

“Kamala Harris is the right person at the right time,” Hoffman, who has given more than $8 million to support Biden this cycle, said. “Harris’s background and leadership growing the economy, fighting for bodily autonomy, and protecting our democracy uniquely position her to push back against Trump’s extremism.”

Though Harris is the most visible potential candidate to replace Biden, there is no guarantee she will be on the ticket, and the party is in uncharted territory as it moves to select a new nominee.

Some labor unions, another key source of support for Democratic candidates, publicly and privately praised Harris’ labor record, including the United Auto Workers. Most were waiting to decide on an endorsement until their executive committees could meet.

The American Federation of Teachers, however, swiftly convened its executive counsel and endorsed the vice president, AFT President Randi Weingarten said on X.

A number of Democratic politicians also quickly endorsed Harris on Sunday, including some who have been discussed as potential running mates for her. They include Arizona Sen. Mark Kelly, Transportation Secretary Pete Buttigieg , California Gov. Gavin Newsom , North Carolina Gov. Roy Cooper and Pennsylvania Gov. Josh Shapiro . Former President Bill Clinton and former Secretary of State Hillary Clinton , the 2016 Democratic Party nominee, also announced their support.

Meanwhile, some donors called for the party to look at its options before nominating Harris.

Reed Hastings , co-founder of Netflix , said in an email that delegates should back whoever is most likely to win the swing states, citing Harris, Michigan Gov. Gretchen Whitmer and Buttigieg as possibilities. “Polling won’t help much because the candidates are largely unknown, so it is political judgment” of party leaders that will matter, he said.

Mark Pincus , the former chief executive of videogame company Zynga, said “Biden stepping aside now gives the Dems at least a chance of winning. My hope is that they commit to a truly open convention.”

Though he has poured millions into Biden’s re-election campaign, Pincus in recent weeks has grown increasingly skeptical of the president’s ability to lead and publicly called for him to step back from the race.

“My greater hope is that they change directions and promote a more mainstream, pro America platform rather than moving further left. At this point I’m undecided,” he said.

Democratic donor and venture capital investor Vinod Khosla also called for an open convention while throwing his support behind Shapiro and Michigan Gov. Gretchen Whitmer.

“Time to have an open convention and get a more moderate candidate who can easily beat @realDonaldTrump …Every socially liberal, climate and fiscal voter should want it to balance our approach,” he said on X.

In Los Angeles, a group of wealthy female donors joined a Zoom call about an hour after Biden’s announcement to discuss how they can support Harris, said Democratic donor adviser Hannah Linkenhoker, who participated in the meeting.

“Donors are excited and ready to back her,” said Linkenhoker. “We are going to bring everything we have to get her elected.”

Write to Emily Glazer at Emily.Glazer@wsj.com , Preetika Rana at preetika.rana@wsj.com , Maggie Severns at maggie.severns@wsj.com and Dana Mattioli at dana.mattioli@wsj.com

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