Billionaire climate activist Tom Steyer, who’s increasingly throwing his weight around in politics, said approving the Keystone XL oil sands pipeline would create political hurdles for President Obama’s second-term agenda and cost him the support of key donors.

Steyer, a major Democratic fundraiser, told Grist magazine that Keystone opponents have leverage to exert over Obama even though he’s free of having to run for reelection.

“If you look at the people who support Obama, and then you look at the people who support him actively and give money, the number of people who care about climate in this second group is actually a majority — not out of the people who support him, but the people who are really active and give money. It’s an enormously high percentage,” Steyer, who made his fortune running a hedge fund, said in the wide-ranging interview.