OAKLAND, Calif. — Robert F. Kennedy Jr. chose Nicole Shanahan on Tuesday to be his vice presidential pick, adding a wealthy but nationally unknown figure to his independent White House bid that's trying to appeal to voters disaffected by a rematch of the 2020 election.

Shanahan, 38, is a California lawyer and philanthropist who's never held elected office. She leads Bia-Echo Foundation, an organization she founded to direct money toward issues including women's reproductive science, criminal justice reform and environmental causes.

Kennedy, a former Democrat, made the announcement in Oakland, Calif., where Shanahan was raised in an impoverished family.

“Nicole and I both left the Democratic Party,” he said. “Our values didn't change. The Democratic Party did.”

Kennedy's campaign has spooked Democrats, who are fighting third-party options that could draw support from President Joe Biden and help former President Donald Trump. But allies for both Biden and Trump attacked Kennedy and Shanahan on Tuesday, reflecting the uncertainty about how Americans might respond to an independent ticket that has little chance of winning Electoral College votes but could draw votes across the spectrum.

Without the backing of a party, Kennedy faces an arduous task to get on the ballot, with varying rules across the 50 states. He's picking a running mate now because about half of the states require him to designate one before he can apply for ballot access.

Kennedy has secured access to the ballot in Utah. He and an allied super PAC, American Values 2024, say they've collected enough signatures to qualify in several other states, including swing states Arizona, Nevada and Georgia, but election officials there have not yet signed off.

In Nevada, Democratic Secretary of State Francisco Aguilar said in a March 7 letter to independent candidates that they must nominate a vice presidential candidate before collecting signatures. The letter came days after Kennedy's campaign announced he'd collected enough signatures in the state.

Kennedy acknowledged the hurdles he faces and urged Americans to “take a risk” and vote for him, saying the biggest obstacle to his campaign is the belief that he can't win.

“If Nicole and I can get Americans to refuse to vote from fear, we're going to be in the White House in November,” he said.

In a nearly 30-minute speech introducing herself to Kennedy supporters, Shanahan echoed the critique at the heart of Kennedy's campaign — that both major parties, the media and the U.S. government are beholden to greedy profiteers. She also embraced his discredited anti-vaccine message.

“It wasn't until I met Bobby and people supporting him that I felt any hope in the outcome of this election,” Shanahan said.

Formerly married to Google co-founder Sergey Brin, Shanahan is deeply enmeshed in the Silicon Valley technology culture that Kennedy frequently critiques.

But he said her connections would help her confront the tech industry's power and influence, and her knowledge of artificial intelligence could steer the government to nurture transformative technologies.

Outside the performing arts venue where Kennedy announced his pick, broken-down cars, discarded bicycles, tents and all manner of household goods took up the sidewalk and a park, a visual reminder of the housing crisis that has plagued California.

Dawn Mitchell, a 52-year-old retired Army reservist and U.S. Postal Service worker from Chesapeake, Virginia, said she was vacationing in Los Angeles when she heard Kennedy would be appearing in Oakland and decided to make the six-hour drive to hear him and Shanahan.

“I didn't really know her before, but just listening to her and listening to her passion about helping children and the chronic disease epidemic and regenerative farming, I'm pretty impressed by her,” she said.

Speakers who entertained the crowd before Kennedy took the stage included Angela Stanton-King, a woman pardoned by then-President Donald Trump for her role in a car theft ring that led to a 2004 federal conspiracy conviction and two years in prison; Metta World Peace, the NBA all-star player formerly known as Ron Artest; and Dr. Jay Bhattacharya, a Stanford Medical School professor who questioned the efficacy of lockdowns during the COVID-19 pandemic and was part of Republican Florida Gov. Ron DeSantis' presidential launch event last year.

The Democratic National Committee is gearing up to take on Kennedy and other third-party options, including No Labels, a well-funded group working to recruit a centrist ticket. The effort is overseen by veteran strategist Mary Beth Cahill, whose resume includes chief of staff to the late Sen. Edward M. Kennedy of Massachusetts, another of RFK Jr.'s uncles.

Some members of his family have publicly criticized his views. Dozens of Kennedy family members sent a message when they posed with Biden at a St. Patrick's Day reception at the White House in a photo his sister Kerry Kennedy posted to social media.

“He's a spoiler. He's tried to coast on his family legacy and the goodwill they have in the African American community,” Pennsylvania Lt. Gov. Austin Davis said of Kennedy on a conference call with reporters organized by the DNC. “But the Kennedy family has denounced this lame attempt and they've quite frankly stood with President Biden.”

Republicans, likewise, worry Kennedy's anti-establishment bent and skepticism about the response to COVID-19 could entice voters who might otherwise vote for Trump.

“Robert F. Kennedy Jr. is a far-left radical that supports reparations, backs the Green New Deal, and wants to ban fracking,” said Alex Pfeiffer, a spokesperson for the pro-Trump super PAC Make America Great Again Inc. “It's no surprise he would pick a Biden donor leftist as his running mate.”

Kennedy is a descendant of a storied Democratic family that includes his father, Robert F. Kennedy, who was a U.S. senator, attorney general and presidential candidate, and his uncle former President John F. Kennedy.

Kennedy was a teenager when his father, known as RFK, was assassinated during his own presidential campaign in 1968. RFK Jr. built a reputation of his own as an activist, author and lawyer who fought for environmental causes such as clean water.

Along the way, his activism has veered into conspiracies and contradicted scientific consensus, most infamously on vaccines.

An anti-vaccine group Kennedy led has a lawsuit pending against a number of news organizations, among them The Associated Press, accusing them of violating antitrust laws by taking action to identify misinformation, including about COVID-19 and COVID-19 vaccines. Kennedy took leave from the group when he announced his run for president but is listed as one of its attorneys in the lawsuit.