Touting himself as an outsider with a proven grassroots organizing record, newly declared Democratic White House candidate Tom Steyer took aim Thursday at some of his top rivals for the party’s presidential nomination

“The top three candidates have been in Congress and the Senate for a combined 70 years,” the billionaire progressive environmental advocate and philanthropist told Fox News on Thursday.

This was a likely reference to former Vice President Joe Biden (a former senator) and Sen. Bernie Sanders, I-Vt., as well as possibly Sen. Elizabeth Warren. But without naming names, Steyer characterized some of the leading contenders for the nomination as insiders and part of the problem.

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Steyer – the 62-year old former hedge fund manager who’s turned into a force in national politics thanks to his creation of the increasingly influential grassroots advocacy group NextGenAmerica – declared his candidacy on Tuesday.

Steyer’s entry into the race – and his vow to spend $100 million of his own money on his campaign – isn’t sitting well with some of his rivals for the nomination, who’ve pledged to rid big bucks from American politics.

"I like Tom, he is a good guy, he’s a friend of mine, but I’m not a great fan of billionaires getting involved in the political process," Sanders said in an interview on MSNBC hours after Steyer launched his campaign.

Sanders is mostly fueling his campaign with small-dollar donations from grassroots contributors and has eschewed fundraisers with top-dollar donors. So is Warren, another populist senator preaching progressive policies who’s among the top tier of Democratic White House contenders.

“The Democratic primary should not be decided by billionaires, whether they’re funding Super PACs or funding themselves,” the two-term Democratic senator from Massachusetts tweeted earlier. “The strongest Democratic nominee in the general will have a coalition that’s powered by a grassroots movement.”

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Another rival, Sen. Kirsten Gillibrand of New York, when asked about Steyer's entry into the race by reporters during a campaign stop in New Hampshire, merely said "God Bless him,” before adding “I know why I’m running.”

Gillibrand then highlighted that she’s “running on the idea that we need publicly funded elections” and argued that “the money interests have a corrupting influence on politics in America.”

Asked about the criticism from some of his rivals, Steyer said in an interview with Fox News and NHTalkRadio.com that “the real question here is not about money or personality. The real question is who has a vision for what we need to do in America and can connect with the American people.”

And he said, “are you going to do the reform from the outside, which is what I’ve been doing for ten years successfully, or are you going to count on an insider to somehow reform the system that’s so badly broken?”

Steyer has also become one of the ringleaders over the past two years in the push to impeach President Trump through his Need to Impeach movement, which he said now has a petition list with 8.2 million signatures.

Arguing that Democrats in the nation’s capital have dropped the ball in moving toward impeachment, Steyer said “the political establishment basically told the millions of people on our petition list ‘we don’t care what you have to say.’ They’re still saying it.”