Hillary Clinton yesterday won the endorsement of billionaire environmental activist Tom Steyer, who has proven himself willing to spend big on candidates and campaigns that back his green agenda.

 "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. "Now is the time to come together to defeat Donald Trump, who is utterly unfit to be our next president."

 That’s surely unwelcome news to Clinton’s constituents in organized labor, who were peeved by Steyer’s opposition to the Keystone XL pipeline, among other stances.

 As the New York Times reported last month, “The building-trade unions view Mr. Steyer’s environmental agenda as a threat to the jobs that can be created through infrastructure projects like new gas pipelines.”

 So deep is the divide between these two Democratic constituencies that it threatened to derail a major get-out-the-vote effort.

 Richard Trumka, head of the laborers union, last month called partnership with Steyer a “politically bankrupt betrayal.” He also wrote, “We object to the political agenda of the A.F.L.-C.I.O. being sold to a job-killing hedge fund manager with a bag of cash,” the New York Times reported.

 As Hillary Clinton became the presumptive nominee yesterday, much was made of the growing rift in the Democratic Party among her supporters and those of Bernie Sanders. But the green-labor division will prove another dilemma for Clinton, especially as Donald Trump makes his pitch to blue-collar workers.