Marco Rubio’s newest big donor could make his life very good—and a little complicated.

Last weekend, New York hedge fund billionaire Paul Singer revealed that Rubio is his pick for 2016. Singer is a rare breed: both a Republican mega-donor and a staunch, open-handed backer of the gay-rights movement.

When it comes to gay rights, Rubio is far from being in lockstep with Singer. The senator has consistently opposed marriage rights for same-sex couples, and he criticized the Supreme Court ruling that said those rights are constitutionally protected. Unlike some Republican contenders—including his Senate colleague Ted Cruz—he hasn’t come out in favor of a constitutional amendment to give states the right to ban same-sex unions. And he told Fusion’s Jorge Ramos in April that he would attend a gay wedding if one of his friends or relatives invited him.

But while he was in the Florida legislature, he opposed efforts to let gay couples adopt kids out of the state’s troubled foster care system.

“Some of these kids are the most disadvantaged in the state,” he said in 2006, when he was Florida’s House majority leader. “They shouldn’t be forced to be part of a social experiment.”

And, ironically, Rubio teamed up with the National Organization for Marriage in 2012 to tape robocalls opposing marriage rights for same-sex couples, according to the Washington Blade. The group also called him a “real marriage champion” in a fundraising letter it sent out this January.

Last month, the National Journal reported that the American Unity Fund—of which Singer is one of several leading center-right donors—has joined with Young Conservatives for the Freedom to Marry to push for the Republican Party to change the platform’s current language so it is neutral about gay marriage, and to add “a new statement on marriage and family that unifies the Republican Party around core values of strong families, limited government, tolerance, and personal freedom,” according to its website. (Full disclosure: The president of the American Unity Fund is Margaret Hoover, the wife of The Daily Beast’s editor-in-chief, John Avlon.)

The campaign, according to the National Journal, will reach out to every Republican state party chair, committeeman, and committeewoman.

Some social conservatives are looking to use Singer’s support to target Rubio. On Monday, Breitbart announced that winning over the billionaire is a “kiss of death” for the Floridian’s campaign. And Brian Brown, who heads the anti-gay marriage National Organization for Marriage, said his organization will consider running ads in Iowa and South Carolina that criticize Rubio for having the donor’s support.

“Rubio being endorsed by someone like Singer is very, very troubling,” Brown said.

Brown and Singer have squared off before.

In 2009, Brown’s group—a group for which Rubio taped robocalls!—lobbied heavily against legislation in New York state that would have let same-sex couples marry. The bill didn’t pass, and they chalked it up as a win. But in 2011, the bill came back with a strong new ally: Singer.

Marc Solomon detailed in his book Winning Marriage how the hedge fund billionaire lobbied Republicans to back the bill. Singer hosted a briefing for hedge fund executives and investors to meet with members of Gov. Andrew Cuomo’s team to strategize about the issue. He and other event attendees raised $1 million to help buy ads to generate support for the legislation. He also met with Republican state senate leaders Dean Skelos and Tom Libous to discuss on how to deal with the issue.

Throughout that effort, Singer worked to shore up Republican support for the bill and raise money to pay for ad campaigns boosting it and its supporters. He committed to helping fund re-election efforts for four Republicans who jeopardized their political futures to vote for the bill.

Brown said that Singer’s involvement was key to the bill’s passage.

“Critical, critical,” he said, of Singer’s impact. “We had stopped it the year before. It was Singer’s money that really changed the situation.”

Frank Bruni wrote at The New York Times that Singer’s fundraising efforts produced the majority of the funding for the state’s marriage equality campaign, and that he’s given upwards of $10 million to such efforts. The New York win was particularly historic, making New York the most populous state in the country to let same-sex couples marry until California caught up two years later. It was just the sixth state to let same-sex couples marry (not counting D.C.), and the win came after advocates for gay marriage faced a string of defeats around the country. The passage of the New York legislation—thanks in large part to Singer—gave their efforts new momentum.

So, the teaming up of a NOM marriage champion with a billionaire who played an outsize role in legalizing gay marriage for millions? It’s the 2016 Republican primary. Par for the course.