Atlanta (CNN) Tom Steyer, the billionaire environmentalist and Democratic mega-donor, says he is considering a run for political office -- and that he sees the United States in a "complete crisis, honestly," under President Donald Trump.

Steyer, who has pumped more than $160 million into Democratic politics through his NextGen America group in the last two election cycles, didn't rule out a run for California governor in 2018 or for the presidency in 2020.

He also acknowledged that his focus -- and that of his organization, which recently rebranded itself to broaden the set of issues it is tackling -- is on national politics.

"I would say it is hard for me not to think about that fight," Steyer said in an interview with CNN reporters at Netroots Nation, a progressive summit being held in Atlanta. He called Trump's presidency a "historic moment" and said America's political divide "is not shrinking, it's growing."

Asked about his thought process as he weighs a run for office, Steyer said: "The way that I think about it is, how can I make the biggest difference?"

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