Sen. Elizabeth Warren Elizabeth WarrenHillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns On The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline Democratic senators ask inspector general to investigate IRS use of location tracking service MORE (D-Mass.) on Tuesday jabbed the latest Democrat to join the 2020 primary, billionaire Tom Steyer Tom SteyerTV ads favored Biden 2-1 in past month Inslee calls Biden climate plan 'perfect for the moment' OVERNIGHT ENERGY: Trump administration finalizes plan to open up Alaska wildlife refuge to drilling | California finalizes fuel efficiency deal with five automakers, undercutting Trump | Democrats use vulnerable GOP senators to get rare win on environment MORE, by saying the election shouldn't be controlled by the wealthiest class.

"The Democratic primary should not be decided by billionaires, whether they’re funding Super PACs or funding themselves," Warren tweeted Tuesday. "The strongest Democratic nominee in the general will have a coalition that’s powered by a grassroots movement."

The Democratic primary should not be decided by billionaires, whether they’re funding Super PACs or funding themselves. The strongest Democratic nominee in the general will have a coalition that’s powered by a grassroots movement. — Elizabeth Warren (@ewarren) July 9, 2019

Steyer, a liberal activist and former hedge fund manager, became the 25th candidate to enter the race Tuesday morning.

He's worth an estimated $1.6 billion, according to Forbes, and he signed the "Giving Pledge" in 2010 along with his wife, making a promise to donate the bulk of their assets to philanthropic causes.

Warren has vowed to not accept money from political action committees and does not hold high-dollar fundraisers.

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She's been successful in her grassroots efforts, raising more than $19 million in the second quarter of 2019 with an average donation of $28. That total places her in the top three among Democrats who have announced their second-quarter numbers.

Sen. Bernie Sanders Bernie SandersThe Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power Bernie Sanders: 'This is an election between Donald Trump and democracy' The Hill's 12:30 Report: Trump stokes fears over November election outcome MORE (I-Vt.) is also running a grassroots fundraising campaign, but he has not raised as much as Warren.

Sanders's campaign said it raised $18 million in the second quarter and transferred another $6 million from other accounts.

Sanders also called out Steyer's campaign on Tuesday, saying "I like Tom personally" but adding that he's "a bit tired of seeing billionaires trying to buy political power."

A spokesman for Steyer told The Hill that the candidate "agrees with Senators Warren and Sanders about the importance of running a grassroots campaign."

"He's been doing that from the outside for the last 10 years, beating big corporations by going directly to the voters," Alberto Lammers said in a statement, noting Steyer's effort to mobilize young voters in 2018.

"Tom's campaign for President will build a national grassroots movement to remove the corrupting influence of corporate money on our politics and push power to the American people," Lammers said.

--Updated at 5:42 p.m.