Earlier this summer, Sen. Elizabeth Warren (D-Mass.) became the spear tip of Hillary Clinton’s campaign, skewering Republican nominee Donald Trump in repeated head-to-head battles on Twitter.

Now, the progressive firebrand appears to be staking out her role in a potential Clinton administration as a bulwark against the influence of Wall Street.

“We believe Sen. Elizabeth Warren is succeeding in establishing herself as the chief financial policymaker in a potential Clinton White House,” Jaret Seiberg, managing director at the financial research firm Cowen Group, wrote in an investor memo on Thursday. “She has threatened to stop Clinton nominees with ties to BlackRock and other firms. And she is using the bully pulpit to shape the debate over the Wells Fargo cross-selling controversy.”

On Wednesday, Warren signaled that she would try to stop any appointment of big bank executives to Clinton’s cabinet. First, she said progressives need to vote Clinton into office. Then, she said she plans to pressure Clinton to fill her cabinet with “advisers who believe in the agenda she has outlined.”

“We don’t mean advisers who just pay lip service to Hillary’s bold agenda, coupled with a sigh, a knowing glance, and a twiddling of thumbs until it’s time for the next swing through the revolving door ― serving government, then going back to the very same industries they regulate,” Warren said in a speech at the progressive think tank Center for American Progress. “We don’t mean Citigroup or Morgan Stanley or BlackRock getting to choose who runs the economy in this country so they can capture our government.”

BlackRock chief Larry Fink has been widely floated as a possible candidate for Treasury secretary. Fink, whose firm is the world’s largest asset manager, wants the job. He controls $4.6 trillion ― about a trillion dollars more than the annual federal budget. Fink almost clinched the position in 2012 after then-Treasury Secretary Timothy Geithner stepped down, and he’s assembled what The Intercept calls “a veritable shadow government full of former Treasury Department officials.”

Hamilton “Tony” James, the president of the private equity giant Blackstone, has likewise been floated for the job. Facebook Chief Operating Officer Sheryl Sandberg’s name also came up last week.

“This is about people who understand the urgency of the need for rebuilding opportunity in America now and who will fight for it with everything they’ve got,” Warren said on Wednesday. “People who will fight for every single promise Hillary Clinton has put forward during this campaign ― including her promise to end the revolving door between Wall Street and Washington.”

Notably absent from her list of personae non gratae was Gary Gensler, the former chair of the U.S. Commodity Futures Trading Commission and a partner at Goldman Sachs.

“Gensler generally enjoys broad support from progressives and is seen as driving the crackdown on derivatives that was included in Dodd-Frank,” wrote Seiberg, the Cowen Group director. “He is also the CFO of Clinton’s campaign.”

Clinton, for her part, has outlined a fairly progressive policy platform in an effort to appeal to fans of Warren and Sen. Bernie Sanders (I-Vt.), who challenged Clinton for the Democratic nomination with calls for systemic financial reform.

“They have taken seriously the need to keep the reform-oriented wing of the party happy enough,” one Warren ally recently told The Huffington Post, “and for now they seem to have succeeded.”

Warren’s speech came a day after she hammered Wells Fargo CEO John Stumpf for his role in a five-year scheme in which thousands of bankers opened more than 2 million accounts for customers without them knowing.

“You should resign,” she told Stumpf, speaking at the Senate banking committee. “You should give back the money you took while this scam was going on, and you should be criminally investigated.”

It’s common for Congressional panels to pick apart scandal-struck corporate leaders. But Seiberg predicts that Warren’s “enormous clout” within the Democratic Party will be amplified as senators begin looking ahead to the 2018 election season.

“Yes, there is always a lot of rhetoric on Capitol Hill,” Seiberg wrote. “But her comments went further than what we typically hear. It shows that she is a master of the bully pulpit. And she can use that to frame the debate.”

“This is why we continue to believe that Clinton will be limited if she wants to moderate policy related to the biggest banks,” he added. “Warren has effectively declared that she has veto power over what Clinton will do.”