Billionaire environmental donor Tom Steyer endorsed Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE for president Wednesday, citing her positions on clean energy and the middle class.

“Hillary Clinton is an experienced leader who will lead us to victory because she embodies the best values of our country,” Steyer said in a statement.

“She will put the needs of working families first. She will be fearless in her pursuit of solutions to the most urgent challenges we face. She will move us rapidly towards becoming ‘the clean energy superpower of the 21st century,’ with inclusive prosperity and a better future for all,” he said, quoting Clinton’s statements on renewable energy.

Steyer had previously hosted a fundraiser for Clinton and complimented her, but had held off on endorsing her. His endorsement came a day after Clinton, the now-presumptive Democratic presidential nominee, won California and three other state contests, cruising to a huge delegate lead over rival Bernie Sanders Bernie SandersNYT editorial board remembers Ginsburg: She 'will forever have two legacies' Two GOP governors urge Republicans to hold off on Supreme Court nominee Sanders knocks McConnell: He's going against Ginsburg's 'dying wishes' MORE.

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Steyer, a former hedge fund manager who lives in the San Francisco area, has donated tens of millions of dollars of his own fortune since the 2014 election to Democratic candidates who want to take bold action on climate change, with mixed success.

He complimented Sanders for his work on climate change and economic inequality.

“His passion for justice sets an example for us all,” said Steyer.

Presumptive GOP presidential nominee Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE, he said, “is utterly unfit to be our next president,” and his “racist rhetoric is directly offensive to our American values, and his dangerous actions would threaten our children’s future in every way.”

Steyer leads the NextGen Climate PAC, which could be primed to help Clinton. It is undertaking a $25 million effort to target millennials on college campuses, the largest college-focused election effort in history.

Steyer launched his 2016 efforts last year by challenging all of the presidential candidates to put forth climate plans that would result in 50 percent of the country’s electricity coming from emissions-free sources by 2030. Clinton, Sanders and former Maryland Gov. Martin O’Malley all complied.

Steyer, who is often compared to the conservative billionaire brothers Charles and David Koch for his fortune and his influence on elections, has promised a suite of other major efforts through NextGen as the campaign season continues.