WASHINGTON (AP) — New York hedge fund billionaire George Soros and Hollywood director Steven Spielberg are among the biggest donors to a super PAC backing Democrat Hillary Rodham Clinton’s presidential run, according to a super PAC official who spoke on condition of anonymity because he was not authorized to discuss fundraising.

In all, the super PAC Priorities USA Action will report having raised $15.6 million in the past three months when it files its fundraising information this month with the Federal Election Commission. Super PACs can take donations of unlimited size. The biggest gift was worth $2 million and came from media mogul Haim Saban, owner of the Spanish-language Univision network.

Donors include film producer Jeffrey Katzenberg, investor Donald Sussman, Boston political activist Barbara Lee and the Plumbers and Pipefitters union. Actress Katie McGrath and her husband, producer J.J. Abrams, also contributed.

The super PAC, which formed in 2011 to help re-elect President Barack Obama, was mostly inactive until Guy Cecil, a former Clinton campaign aide, came aboard in May. His leadership helped cement Priorities as the go-to super PAC for Clinton and sparked a burst of fundraising. Priorities landed 80 percent of its contributions in just the last four weeks, according to an email Cecil sent Thursday to supporters.

Although Clinton is the front-runner in a small Democratic primary, her boosters say she’ll need big money_including from super PACS_to fend off attacks from a huge field of Republican competitors. Priorities officials anticipate raising far more than the $79 million the super PAC brought in to help Obama.

“It may seem early to many of us, but with the amount of money pouring in from the far right wing, the time has come for our side to kick things into high gear,” Cecil wrote in the email.

On the GOP side, former Florida Gov. Jeb Bush will benefit from a super PAC called Right to Rise, which is expected to report having raised about $100 million since the start of the year. Another presidential candidate, Texas Sen. Ted Cruz, boasted last month that between his campaign and the outside groups helping him, his supporters have given more than $40 million.

The Republicans will deploy much of their money to win the competitive primary, but still more outside groups have said they will devote their resources to defeating the Democratic nominee. Chief among those forces is an $889 million network of policy and political groups financed by billionaire energy executives Charles and David Koch and other wealthy donors who want a smaller federal government.

Clinton’s campaign reported Wednesday it has raised $45 million since she declared her candidacy in mid-April.