Billionaire climate activist Tom Steyer has been the largest single political donor in the last two election cycles, spending more than $166 million on liberal causes and candidates, according to campaign finance data.

Steyer spent more than $91 million in the 2016 election cycle and more than $75 million in the 2014 cycle, according to the Center for Responsive Politics.

And that doesn’t include the estimated $20 million Steyer is said to have spent on TV and digital ads calling for the impeachment of President Donald Trump.

Now, he’s built an email list of nearly 4 million Americans as part of that campaign, according to the campaign’s website NeedToImpeach.com. That’s fueling speculation he will run for political office, and maybe even president.

“I think it begs the question of whether or not he’s running for president in 2020,’’ Democratic consultant Dave Jacobson told Politico Wednesday. “He’s set his sights on building up a national apparatus; he’s capitalizing on the new norm, which is digital persuasion.’’

“That’s how you build a grass-roots operations for a presidential campaign,” echoed Republican strategist Mike Madrid.

“That’s what he’s building, and it’s probably second only to Bernie Sanders’ list, and may be eclipsing it,” Madrid said, according to Politico. “Every election cycle has its own dynamics, and whoever is tapping into the sentiments of their own base usually has an advantage.”

While Steyer’s focus is now impeachment, he got his start in national politics funding environmental campaigns, including bankrolling much of the anti-Keystone XL oil pipeline effort. Steyer’s a long-time political donor and bundled donations for Hillary Clinton’s 2016 presidential run.

The former hedge fund manager then funded the political group NextGen Climate Action with the goal of making global warming a top-tier election issue. That largely failed despite millions being poured into it, and Steyer broadened its mission earlier this year.

Political pundits have been speculating about Steyer’s political ambitions for years. Why else would a retired billionaire inject himself into political ads?

Steyer himself hasn’t been shy about a potential run for office, recently telling C-SPAN, “I haven’t ruled it out, and I’m actually trying to determine what will have the most positive differential impact.”

“I’m absolutely ambitious,” Steyer told C-SPAN is a soon-to-air-interview, “to try and be part of the group of people who gets America back on a just and prosperous course.”

So far, most Democratic lawmakers haven’t backed efforts to impeach Trump, and instead are waiting for the Special Counsel Robert Mueller to finish his investigation. Only 58 House Democrats backed Louisiana Rep. Al Green’s impeachment legislation introduced in December.

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