As he cut into steak frites at the recent fund-raiser he hosted for Robert F. Kennedy Jr.’s long-shot bid for the Democratic presidential nomination, the financier Omeed Malik surveyed the crowd.

What he saw on that July evening was unusual, he said: Environmentalists and admirers of Mr. Kennedy’s family were mingling at a restaurant in Sag Harbor, N.Y., alongside Hollywood figures, hippies and right-wing conservatives.

“It was a complete hodgepodge of characters that I have never seen at a political event,” recalled Mr. Malik, an investor and merchant banker based in Palm Beach, Fla. “Because everyone is attracted to him for a different reason.”

Fueled by an unusual combination of views — passionate environmentalism, for example, alongside a deep distrust of the pharmaceutical industry and public health orthodoxy — Mr. Kennedy’s campaign has stood out for its curious coalition of Democrats, Republicans and independents of varying backgrounds.

Financial filings this week from two super PACs supporting him, which together have raised nearly $10.5 million, seemed to underscore this theme. The pro-Kennedy super PAC American Values 2024 received the bulk of its money from two megadonors: one who has contributed tens of millions to Republican causes, and another who has backed both Democrats and Republicans.

Timothy Mellon, a Wyoming Republican who contributed $53 million in stock to a Texas fund paying for construction of a new border wall, gave that super PAC $5 million. Gavin de Becker, a security executive who describes himself as a Democrat and consulted for the Amazon founder Jeff Bezos during Mr. Bezos’s text message scandal, donated $4.5 million.

“The fact that Kennedy gets so much bipartisan support tells me two things,” Mr. Mellon, previously a top donor to former President Donald J. Trump, said in a statement issued by American Values 2024. “That he’s the one candidate who can unite the country and root out corruption, and that he’s the one Democrat who can win the general election.”

In 2019 and 2020, Mr. Mellon gave $70 million combined to super PACs pushing for Republican control of the House and Senate and to one supporting Mr. Trump, records show.

The support from Republicans is likely to heighten suspicions about Mr. Kennedy’s candidacy among Democrats who see him as a pawn in an effort to undermine President Biden. Dozens of venture capitalists, tech executives, real-estate builders and investors with varying political alliances also contributed to the Kennedy-aligned PACs.

Patrick Byrne, the former chief executive of Overstock.com — and one of the most prominent supporters of the effort to overturn the 2020 election — gave $100,000 in Bitcoin to Common Sense, another PAC supporting Mr. Kennedy.

Abby Rockefeller, a daughter of the investment banker David Rockefeller who runs a cannabis farm in upstate New York, gave $100,000 to the American Values 2024 PAC. She said in a statement that she always voted for Democrats.

Common Sense reported a total fund-raising haul of about $711,000 in the three-month period ending in June.

Mr. Kennedy, an environmental lawyer, the scion of a storied American political dynasty and a hero of the so-called medical freedom movement — which has seeded public skepticism about vaccines and other public health measures — is unlikely to prevail in his quest for the Democratic nomination.

More than five months before the Iowa caucuses, he is trailing far behind Mr. Biden. He has the support of just 13 percent of registered voters compared with Mr. Biden’s 64 percent, according to a recent New York Times/Siena poll.

And his financial support is likely to pale in comparison with the powerhouse of fund-raising and institutional support behind the incumbent president.

But the fact that some of deep-pocketed supporters include some who favored Mr. Trump in the past suggest that those numbers may have room to grow.

“I don’t think he has the influential tech leaders,” said Charles Phillips, a venture capitalist who co-founded a nonpartisan PAC to support candidates with strategies for economic growth in Black communities. Mr. Kennedy, he added, “won’t get broad support. Most of the tech guys supporting him are really Republicans.”

Mr. Mellon, the grandson of former Treasury Secretary Andrew W. Mellon, also gave $5 million last quarter to the Congressional Leadership Fund, a super PAC dedicated to electing Republicans to the House of Representatives, and $1 million to Fair Courts America, a committee backed by other major Republican donors that has supported conservative candidates for state supreme court seats.

Some of Mr. Kennedy’s smaller-scale supporters said their admiration was driven by Mr. Kennedy’s unfiltered quality as well as his willingness to take on legacy institutions like the mainstream news media (which he says has censored him), the banking system (which he believes takes advantage of consumers), the medical establishment (he has said that big government has been co-opted by the pharmaceutical industry), and the government’s response to Covid-19, which he has said was both overreaching and ineffective.

Some are willing to set aside his more extreme views — including his vaccine skepticism and his conspiracy theories about anti-depressants and “Deep State” corruption — because they admire what they see as his integrity.

The Sag Harbor dinner last month drew more than 30 attendees who each pledged $6,600 to Mr. Kennedy’s campaign, the maximum amount that can be contributed by individuals to a campaign for a primary and a general-election bid combined, according to Mr. Malik. During the evening, Mr. Kennedy took questions on subjects including Russia’s war in Ukraine and cryptocurrency.

In June, Common Sense PAC hosted a fund-raiser in San Francisco with two tech investors, David Sacks — a Silicon Valley entrepreneur and Republican donor who has supported Gov. Ron DeSantis of Florida — and Chamath Palihapitiya, a former senior executive at Facebook.

Nick Corasaniti contributed reporting.