KCBS_740 SAN FRANCISCO (KCBS) — A San Francisco billionaire is taking much of the credit for registering more than a million new voters this year, most of them in California.

Tom Steyer, the hedge fund manager turned environmental activist is the single biggest spender in American politics this year.

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By the time he’s done, Steyer will have spent more than $75 million on this year’s elections – much of it on ads, starring him, to mobilize millennials for progressive causes.

Steyer’s NextGen Climate has registered almost 750,000 new California voters this year.

Steyer tells KCBS this is about empowering a new generation, not raising his own profile.

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“Everything that we’re doing, I’m extremely proud of. Everything we’re doing stands on its own,” Steyer said.

His moves suggest Steyer will run for Governor in 2018, although he tells KCBS he’s not ready to make that decision.

“Until November 8th, there’s no reason to do anything but what we’re doing. We’ve set up these programs, and we want to finish strong, and we want to make sure that we accomplish what we set out to do, and that we feel good about it,” Steyer said.

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Steyer’s progressive activism is at odds with some of his past investments in tobacco companies and private prisons – rich fodder for his opponents if he does run.