Democrat Ben Jealous, accompanied by Sen. Bernie Sanders (I-Vt.), speaks to the crowd during a campaign rally in downtown Silver Spring, Md., on June 18. (Jose Luis Magana/AP)

Six wealthy liberals, all but one from California, have contributed $600,000 to two of four political action committees supporting Ben Jealous in the Maryland Democratic gubernatorial primary, highlighting how large, outside donors are increasingly influencing campaigns far from home.

The individuals’ contributions, together with nearly $900,000 from labor unions, have given the Jealous campaign a significant financial edge over most of his five main rivals, and especially over his principal opponent, Rushern L. Baker III, in advance of Tuesday’s election.

Such outside financing is a novelty in a gubernatorial race in Maryland, although it was a factor in the state’s Democratic U.S. Senate primary in 2016. If Jealous, a former NAACP president, wins the nomination, the PAC support risks opening him to criticism about out-of-state donors from Gov. Larry Hogan (R) in the general election, analysts said.

The four PACs, which are barred by law from coordinating with the Jealous campaign, are using the money for television and radio advertising, mailers, canvassing and other get-out-the-vote efforts.

PACs affiliated with Working Families Party, Progressive Maryland and Our Revolution Maryland say they are spending about $500,000 to boost Jealous.

Gubernatorial candidate Richard S. Madaleno Jr. criticized the outside money being used to support his rival, former NAACP chief Ben Jealous. (Astrid Riecken/For The Washington Post)

The fourth entity is a super PAC called Maryland Together We Rise, which is spending more than $1 million. It is getting money from labor groups and five of the wealthy individuals; the sixth person contributed to Progressive Maryland.

The amount of PAC spending on Jealous’s behalf is “highly unique” in a Maryland governor’s race, said Keith Haller, a pollster and independent political analyst.

The funding drew strong criticism from one of Jealous’s primary opponents, state Sen. Richard S. Madaleno Jr. (Montgomery), who asked, “Who is Ben Jealous going to be held accountable to? Maryland voters or his billionaire bosses?”

But a Jealous spokesman said the contributions showed Jealous would be better able to compete in the fall with Hogan, who has about $9.4 million in his campaign coffers, more than all six Democrats combined.

“The Democratic nominee will start out at a financial disadvantage to Hogan, so having a candidate with the ability and appeal to reach donors large and small in Maryland and nationally is an asset, one that Baker clearly doesn’t have,” Jealous spokesman Kevin Harris said.

As in past elections, both Hogan and the Democratic nominee are expected to benefit from support from their parties’ national governors associations.

Jealous also has more money from his own fundraising than Baker — just under $400,000 on hand, compared to $170,000 for Baker — according to the most recent fundraising reports, released June 15. A June 5 Washington Post-University of Maryland poll showed the two are the front-runners, well ahead of the rest of the field, but with a large number of voters undecided.

Under state law, no individual can contribute more than $6,000 directly to a candidate, but contributions to PACs are unlimited.

Most of the big individual contributors to Maryland Together We Rise are well-known donors from Northern California who have given to many other Democratic campaigns.

One is a surprise — Alexandra Clancy, the fashion designer and widow of spy-thriller author Tom Clancy.

Clancy, who lives in New York and contributed $50,000, declined to comment.

The largest single donor, with contributions totaling $250,000, was Susan Sandler, a San Francisco resident and heiress to a banking fortune. She and her husband, Steve Phillips, founded the Sandler Phillips Center, which advises donors to progressive politicians on how to maximize the impact of their contributions.

The center’s website describes Sandler as “the first and largest donor behind the independent efforts to support Barack Obama’s 2008 presidential campaign.”

She also has been a major contributor to PACs backing Sens. Kamala D. Harris (D-Calif.) and Cory Booker (D-N.J.) — both of whom have endorsed and campaigned with Jealous.

A PAC disclosure initially reporting that a $100,000 contribution came from Phillips was later amended to say that it came from Sandler.

Sandler contributed to the pro-Jealous PAC because Jealous “has been a national social justice leader and anti-poverty crusader for decades,” said Emi Gusukuma, the center’s executive vice president.

Gusukuma said Sandler also liked Jealous’s work advocating in Maryland and elsewhere on behalf of “the Dream Act, marriage equality and ending the death penalty,” as well as increasing voter participation among racial minorities.

Another donor, Mitchell D. Kapor, is managing partner of the venture capital firm Kapor Capital, where Jealous is also a partner.

Kapor, founder of the Lotus computer software company, said it’s rare for him to give money to a PAC because, in general, “Politics is broken and the funding is broken.” He made an exception in this case, donating $50,000 to the pro-Jealous PAC, because of his personal familiarity with Jealous and because Phillips, a friend, asked him to do so.

The other two big donors to Maryland Together We Rise are Quinn Delaney, founder of the Akonadi Foundation, which she and her husband launched “as an outgrowth of their commitment to racial justice”; and Mark Heising, who has given more than $500,000 since 2008 to mostly Democratic candidates and PACs.

Heising’s daughter, Caitlin Heising, contributed $50,000 to the Progressive Maryland PAC.

Delaney and the Heisings did not respond to requests to comment.

When asked about the outside money, Madeleine Russak, a spokeswoman for the Baker campaign, did not mention the individual contributions to the PACs.

But she faulted Maryland Together We Rise, which also gets money from unions, for sending mailers and Facebook videos that attacked Baker’s record on education during his two terms as Prince George’s County executive.

“Labor’s involvement in campaigns isn’t unusual,” Russak said. “However, spending their members’ money to demonize Mr. Baker . . . is more typical of [Republican strategists] Karl Rove and [the late] Lee Atwater than fulfilling a responsibility to make sure voters have the information needed to honestly make the best decision on Election Day.”

Harris disputed the criticism, saying, “It’s not negative campaigning if it’s true.”

Alice Crites, Arelis R. Hernández, Julie Tate and Ovetta Wiggins contributed to this article.