Vice President Kamala Harris on Sunday morning had multiple phone conversations with President Joe Biden before he announced that he would not be seeking reelection and would instead endorse her, according to a source familiar with her schedule.

Surrounded by family and staff at the vice president's residence, Harris spent more than 10 hours placing calls to over 100 party leaders, members of Congress, governors, labor leaders and leaders of advocacy and civil rights organizations. On each of those calls, Harris made clear that she was extremely grateful for the president's endorsement but plans to work hard to earn the Democratic nomination in her own right, the source said.

One of the calls was to her pastor, Amos Brown III, who, along with his wife, prayed over her, according to the source.

The vice president wore a hooded Howard University sweatshirt, workout sweats and sneakers throughout the day. Amid the many calls, she took time to arrange both lunch and dinner for the assembled aides. The menu was salad and sandwiches for lunch and pizza and salad for dinner. Harris' pizza came with anchovies, her go-to topping, the source said.

-ABC News’ Gabriella Abdul-Hakim, Fritz Farrow and Will McDuffie

The Democratic National Committee's next rules committee meeting will be at 2:00 - 5:00 p.m. ET on Wednesday, July 24, a source told ABC News. The meeting will be public and available on the DNC's YouTube page.

The co-chairs announced Sunday that following the President’s decision, it is now the committee's responsibility to implement a framework to select a new nominee, which will be open, transparent, fair and orderly.

The co-chairs announced that the process presented for consideration will be comprehensive and expeditious.

-ABC News' Gabriella Abdul-Hakim

Democratic National Committee Chair Jamie Harrison and Minyon Moore, the DNC convention chair, just sent members a note, obtained by ABC News, saying guidance on the formal nomination process following President Joe Biden's exit from the race will arrive "in the coming days."

“While this situation is unprecedented, the DNC is ready to undertake a transparent and orderly process to move forward as a united Democratic Party and select a nominee," they said in their message. "This process will be governed by rules and procedures of our Party, and we know that all of you are ready to take your responsibility seriously to swiftly nominate a candidate who will defeat Donald Trump in November. In the coming days, you will hear more from us on the next steps to formally select our nominee. As we move forward, our values as Democrats will remain the same – protecting our basic freedoms, fighting for working families, and saving our democracy from the threat of dictatorship."

The pair said the DNC will "honor" Biden's "legacy with a firm commitment to nominating and electing a Democratic president this November" who will continue the strides he has made as president.

As of Friday, Democrats planned to continue their virtual nomination process to ensure that Biden and Harris were on the ballot in all 50 states. That was, of course, before Biden made his announcement on Sunday afternoon.

-ABC News' Brittany Shepherd

The United Auto Workers Union has reacted to the news that President Joe Biden has endorsed Vice President Kamala Harris for president.

While calling Harris an "ally," the UAW spokesperson stopped short of offering an endorsement, noting its board will meet soon.

In a statement to ABC News, a UAW spokesperson said, "Our UAW International Executive Board, elected by the membership of the UAW, will meet in the coming days to decide our next steps. Vice President Harris has been an ally and a champion for the UAW and the whole working class, and we're excited to defeat Donald Trump and the billionaire class at the ballot box this November."

The UAW had endorsed Biden for president earlier this year.

-ABC News' Briana K. Stewart