At Bill de Blasio’s inauguration, no one stole the new mayor’s spotlight—not Harry Belafonte’s unhistory, not “Imagine” unplugged, not even a former president. The only person who came close was Letitia James, who was sworn in as public advocate. Clad in a bright red coat, powerfully postured and—incredibly—with Dasani Coates in tow, her inaugural address was a frontal assault on the Bloomberg legacy.

In the forty-eight hours since the festivities on the City Hall patio, James has had to clarify remarks that seemed to suggest she was a source for the December New York Times series that profiled Coates, one of the city’s 20,000 homeless youth. And de Blasio has rebuffed suggestions that his swearing-in ceremony was over the top in its Bloomberg-hating.

What’s received less attention, but might be more interesting, was the warning James issued toward the end of her speech.

"All of us share a progressive vision for this city’s future,” she said as she congratulated de Blasio and Comptroller Scott Stringer. She pledged to work with her two fellow city officials. Then she said, “Of course, if working people aren’t getting their fair share, if our government isn’t securing the reforms New Yorkers were promised, you better believe Dasani and I will stand up—that all of us will stand up—and call out anyone and anything that stands in the way of our progress.”

The question is, Who did the public advocate mean by “all of us” who are going to stand up, and who are the “anyone” who might stand in the path of progress? Could the new mayor himself get called out at some point?

In theory, at least, that’s James’s new job. The city’s number-two official, the public advocate takes over temporarily if the mayor cannot serve, presides over full City Council meetings, can gather information from city agencies, has the right to propose legislation and makes appointments to some city boards. Its role is sometimes defined as that of an ombudsman: someone to look out for the little guy and monitor the operation of city government. But in New York’s strong-mayor system, the advocate is also positioned as a check and balance on the mayor.

The office has little statutory power and a very modest budget, so when it has wielded influence it has done so through its media profile and largely through its adversarial role at City Hall. The first public advocate, former consumer affairs commissioner Mark Green, was the perfect progressive adversary to the conservative Giuliani administration from 1994 through 2001; he made ample use of the bully pulpit, generated a lot of headlines and was a reliable thorn in Rudy’s side.

Betsy Gotbaum, a former city parks commissioner, tried a more conciliatory approach during the first Bloomberg years and was not rewarded for the effort. Hobbled by her paltry budget, even the more aggressive Gotbaum of later years never got the ink that Green had enjoyed, although she was a consistent voice for enlightened policy. De Blasio succeeded Gotbaum in 2010. His office issued dozens of solid reports, but de Blasio’s well-known designs on the mayoralty cast all his actions in a campaign context.

So James is in a unique position: she’s the first public advocate to serve alongside a mayor with whom she is largely ideologically aligned. Though James and de Blasio were on opposite sides of the Atlantic Yards controversy, and while James opposes and de Blasio supports the Bloomberg soda ban, the two have often been allies. In 2008 they were the faces of the opposition on the City Council to the mayor’s proposal to overturn term limits. They endorsed each other this fall.

In campaign debates this year, James said she supported de Blasio but pledged to operate independently. At her inauguration day reception, I asked one of her campaign volunteers, Erl Kimmich, what he thought that would mean. “I think they can really work together. There are so many elements of power in New York City—financial power, all the institutions that are already existing,” he said. “With her as public advocate, I think that she can help focus the energies of the grassroots.”

In other words, the public advocate could be a kind of organizer in chief. Bronx Borough President Ruben Diaz Jr., also at the reception, put a slightly different spin on it. “She has an uncanny ability to know what the ground level is feeling and saying,” he said of James. “Not just Bill de Blasio, but the City Council, all public officials—sometimes you lose sight of that.”

So that, according to Diaz, is what James will provide to the mayor—political street recon to keep him on track.

With her reference to calling people out, does James have something a little more aggressive in mind? Progressives love the FDR quote about the importance of pressuring the pols we agree with. “I agree with you, I want to do it, now make me do it,” the late prez said; President Obama paraphrased it seventy years later, and progressives in New York recognize they’ll sometimes need to have de Blasio’s back, and sometimes need to shove it.

Lack of power and shaky media reputation or not, James could be the shover in chief. She’s no stranger to combat—winning a vacant Council seat in 2003 by beating the brother of the assassinated councilman who vacated it, and doing so with only the backing of the Working Families Party; jousting (often breathless with what seemed like barely suppressed rage) with Bloomberg commissioners for years as a councilwoman; winning a public advocate’s race that she was counted out of early on. It will be interesting to see whether James can go from throwing body blows to the more nuanced art of grappling. As de Blasio watched James return to her seat—hand-in-hand with her new “BFF”—after her final fusillade at the Bloomberg administration, a page was turned: the next mayor in James’s cross hairs, if it ever comes to that, will be Bill de Blasio.