Aware that his age could be a concern to some voters, Biden, 77, has said that he is “a bridge” to a new slate of Democratic leaders, and by selecting Harris, more than 20 years his junior, he has elevated a leading figure from a younger generation within the party.

Biden’s selection unfolded with the utmost secrecy after a period in which he spoke with the contenders either in person or in face-to-face meetings. He notified several close advisers on Tuesday, two people familiar with the matter told CNN. After considering some 11 women for the post, he and his aides spent time on Tuesday afternoon notifying the vice presidential prospects who he did not choose.

His calls included California Rep. Karen Bass, the chairwoman of the Congressional Black Caucus, as well as Georgia Democrat Stacey Abrams, Illinois Sen. Tammy Duckworth, Massachusetts Sen. Elizabeth Warren, New Mexico Gov. Michelle Lujan Grisham and Florida Rep. Val Demings, sources familiar with the matter told CNN.

As part of the selection process, the former vice president spoke directly to the final contenders, according to people familiar with the process, through either face-to-face meetings or remote conversations. Officials would not say which of the candidates visited Biden in person, but CNN confirmed last week that Michigan Gov. Gretchen Whitmer had flown to Delaware for a meeting. Harris and former Obama national security adviser Susan Rice were among the others seen as the most serious contenders.

CNN had previously reported that Biden was also believed to be considering Bass, Sen. Elizabeth Warren of Massachusetts and Sen. Tammy Duckworth of Illinois, people familiar with the search say.

In another sign that the pick was imminent, a Biden campaign official told CNN on Tuesday that they have assembled the staff for Biden’s future running mate.

Karine Jean-Pierre, who joined the Biden campaign as a senior adviser in May, will lead the Harris’ team as chief of staff. Jean-Pierre had previously worked for Barack Obama and Martin O’Malley’s presidential campaigns.

Two veterans of the Obama-Biden administration are also joining the team. Liz Allen, who served as deputy communications director for Biden as vice president as well as deputy communications director in the White House, is joining as communications director to Harris. And Sheila Nix, who was chief of staff to Biden’s reelection campaign in 2012 and served as Jill Biden’s chief of staff in the White House, will be a senior adviser to Harris and her husband, Douglas Emhoff. The vice presidential pick is expected to also add a few of her own advisers to the team.

The last time Biden and Harris shared the stage was March 9 in Michigan, the eve of a primary that would prove decisive in Biden’s primary battle. On a stage in a Detroit high school gymnasium, Biden gestured to Harris, Whitmer and New Jersey Sen. Cory Booker and called himself a “bridge” to “an entire generation of leaders” within the Democratic Party.

The spouses of Biden and Harris, Jill Biden and Emhoff, had an exchange over Twitter as Biden welcomed Harris to the ticket.

“Hey @DouglasEmhoff Are you ready?” Jill Biden tweeted.

“America, let’s do this!” Emhoff said.

Progressives also quickly welcomed Harris to the Democratic ticket. Vermont Sen. Bernie Sanders tweeted that Harris “will make history as our next Vice President.”

“She understands what it takes to stand up for working people, fight for health care for all and take down the most corrupt administration in history. Let’s get to work and win,” he said.