Billionaire environmental activist Tom Steyer isn't ready to endorse Hillary Clinton Hillary Diane Rodham ClintonHillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters FBI chief says Russia is trying to interfere in election to undermine Biden MORE in the Democratic presidential primary and is open to supporting Sen. Bernie Sanders Bernie SandersMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters Why Democrats must confront extreme left wing incitement to violence MORE (I-Vt.) if he's the party's nominee.

"Our real goal has been not to support any one candidate, but to emphasize and highlight the issue (of climate change) so that the candidates can lay out their solutions and so the American people can have a chance to make a decision," Steyer, a Democratic mega-donor, told Reuters in an interview published Wednesday.

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"We have always come out and supported the climate champion," Steyer said of the eventual Democratic nominee. "The idea that for some reason we wouldn’t do that, I’d have to understand why in hell we didn’t. Because that has been our practice always."

Sanders appears to have opened up a lead in the early-voting state of New Hampshire, while Clinton is battling the senator in Iowa ahead of the caucuses there Feb. 1.

Steyer, who has raised money for Clinton's campaign and has sought to put a focus on climate change in the Democratic primary, told Reuters that he didn't think Clinton has "fully fleshed out everything she has to say about energy and climate."

"What Bernie Sanders is talking about, which is trying to get back to a more perfect democracy, is something that we support too," the Democratic donor added. "We just think that the idea of ... wishing the rules were different and then pretending they were, is something which, unfortunately, probably would be disastrous from the standpoint of energy and climate," Steyer told the news service.