Independent candidate Robert F. Kennedy Jr will announce his U.S. vice presidential pick on Tuesday in California from a list that includes National Football League star Aaron Rodgers and California-based lawyer Nicole Shanahan.

Kennedy, 70, a scion of the famous U.S. political family, is hoping to use the selection to help build credibility and momentum in his long-shot bet that Americans are so frustrated with Democratic President Joe Biden and his Republican rival Donald Trump that they will pick a third party.

Kennedy has reportedly talked with Rodgers and former Minnesota Governor Jesse Ventura - along with a long list of others - but most political analysts expect him to choose Shanahan, who would bring little Main Street name recognition to Kennedy's ticket, but potential financial firepower.

Shanahan, president of Bia-Echo, which invests in helping women bear children at older ages, criminal justice reform and the environment, has connections in the tech industry and reproductive rights activism. She was previously married to Google co-founder Sergey Brin.

"Kennedy is already seen as a political outsider, and it seems he thinks this is where he has the most advantage," presenting himself outside the political mainstream, said Matthew Green, a politics professor at Catholic University.

Kennedy is backed by 15% of registered voters, versus 39% for Biden and 38% for Trump, according to a recent Reuters/Ipsos poll. The Democratic National Committee and many political strategists say Kennedy's campaign could be a "spoiler" in the 2024 election that would help elect Trump.

Kennedy is announcing now because many U.S. states require independent candidates to name their vice presidential nominees before they start the expensive, time-consuming and varied process of getting on state ballots.

Shanahan did not respond to requests to comment from Reuters.

Kennedy, an environmental lawyer who spent years pushing anti-vaccine messages, told Reuters in an interview last week that he was looking for a running mate who shares his perspective on issues like ending the U.S. "war machine," bringing down the national debt and "ending the chronic disease epidemic."

"I am looking for somebody who has good values, who has an open mind, who has high intelligence and inquisitive curiosity," he said, adding that it was important to find somebody outside of the political system.

Kennedy has collected the required amount of signatures to get on the ballot in four states, but a petition in Nevada is being contested. No Labels, another independent group this election cycle, is on the ballot in 18 states, though it has not yet announced its ticket.

Kennedy's campaign has raised over $27 million this election cycle, and American Values 2024, a super PAC that supports Kennedy's candidacy, has raised over $42 million, according to Federal Election Commission data.

"We're not associated with a major political party, so in a lot of ways this announcement is as close to a kickoff of a run down to the general election as anything," Mark Gorton, co-founder of American Values 2024, told Reuters. "I'm hoping there's a lot of excitement generated."

American Values 2024 plans to hold a fundraiser in San Francisco on Tuesday night.

Kennedy's policy proposals include a pledge to make home ownership easier and a crack down on corporate subsidies, which have helped him gain some traction among voters. (Reporting by Alexandra Ulmer and Stephanie Kelly; Jarrett Renshaw contributed to this story. Editing by Heather Timmons and Alistair Bell)