(CNN) Elizabeth Warren came out swinging on Thursday as the Democratic primary slugfest heats up with Iowa on the horizon.

Speaking in New Hampshire, the Massachusetts senator ramped up what has been a stop-and-go process of directly criticizing her top moderate rivals, taking a series of unmistakable shots at South Bend, Indiana, Mayor Pete Buttigieg and former Vice President Joe Biden. Former New York City Mayor Michael Bloomberg, too, came into her crosshairs.

The common theme: Their reliance on campaign cash from rich donors -- or, in Bloomberg's case, his own bank account -- makes them untrustworthy and unlikely to spend political capital on policies that benefit the working class at the expense of wealthy contributors. Warren herself has sworn off big donors in the primary.

The address came at a critical juncture in Warren's presidential campaign -- after a months-long hot streak, her political momentum appears to have stalled. Buttigieg, despite their ideological differences, appears to have cut into what had been shaping up as her base.

Warren's feud with Buttigieg has recently centered on transparency about their records in the private sector, and in her remarks at the New Hampshire Institute of Politics, she delivered some of her most cutting lines to date. Throughout the campaign, Warren has warned of the corrosive influence of the "wealthy and well connected." Buttigieg, who in recent months has emerged among the front-runners in Iowa and New Hampshire, has been tapping them for campaign cash, which has invited a wave of attacks -- and protests -- from activists on the left.

"We know that one Democratic candidate walked into a room of wealthy donors this year to promise that 'nothing would fundamentally change' if he's elected president," Warren said of Biden, before turning her attention to Buttigieg's fundraising program.

Without naming the South Bend mayor, she continued: "We know that another calls the people who raise a quarter of a million dollars for him his 'National Investors Circle,' and he offers them regular phone calls and special access. When a candidate brags about how beholden he feels to a group of wealthy investors, our democracy is in serious trouble."

In a statement issued shortly after Warren concluded her remarks, Buttigieg senior adviser Lis Smith accused the Massachusetts senator of stoking a potentially damaging intra-party conflict.

"Senator Warren's idea of how to defeat Donald Trump is to tell people who don't support her that they are unwelcome in the fight and that those who disagree with her belong in the other party," Smith said. "We need to move beyond the politics and divisiveness that is tearing this country apart and holding us back. Pete will be a President who will heal our divides and rally Americans around big ideas to solve the problems that have festered in Washington for too long."

Warren has called on Buttigieg to resume naming his bundlers, or the people who work to collect big donations on his behalf and deliver them in chunks to the campaign. After resisting at first, he gave way earlier this week and pledged to make them public. The decision came at around the same time McKinsey, the consulting giant and his former employer, released the 37-year-old from a nondisclosure agreement and allowed him to share the names of clients with whom he worked during his time there.

Progressives hit back at Buttigieg

The more intense focus on Buttigieg's past work and his fundraising practices has also drawn the aggressive ire of progressive activists, who have tried to disrupt a pair of fundraisers he attended this week in New York City. On Wednesday night, at least one protester from a group called New York Communities for Change actually made his way inside one of the events. Outside, demonstrators shouted "Wall Street Pete" at the candidate as he made his way into a waiting car when it was over.

But the beef -- between Buttigieg and progressives like Warren and Sen. Bernie Sanders -- hits at the core of the Democratic Party's ideological divide. Though Warren and Buttigieg are competing for many of the same voters, at least in Iowa and New Hampshire, they have significantly different policy agendas and political philosophies.

Buttigieg blew open the rift with a recent viral Iowa ad in which he denounced plans for tuition-free public college by suggesting they risked "turning off half the country" and argued that taxpayer money shouldn't be used to pay tuition for "the kids of millionaires."

Warren on Thursday addressed the argument, if not the candidate, by name.

"Unlike some candidates for the Democratic nomination," she said, "I'm not betting my agenda on the naive hope that if Democrats adopt Republican critiques of progressive policies or make vague calls for unity that somehow the wealthy and well-connected will stand down."

Warren doubled back throughout the speech in an effort to, for anyone who was not yet clear, underscore the heart of her argument -- that government corruption has allowed for big business and financial industry interests to run roughshod over ordinary Americans.

Bloomberg's decision to enter the primary has provided Warren with what she presents as an abject lesson in that regard. Bloomberg, a billionaire dozens of times over, has already spent tens of millions on television ads and early campaign infrastructure.

"I am no fan of fan of Michael Bloomberg. That has been made clear throughout the years. But here's the deal, Michael Bloomberg built a successful business and I want to honor that," she said on Thursday, making a pitch for her popular -- with voters in recent polling -- wealth tax proposal into an attack on the former mayor. "A wealth tax on millionaires and billionaires isn't about being punitive or denigrating success. It's about laying the foundation for future successes. It's about making sure that the wealthy don't pull the ladder after them."

For most of this year, Warren has declined to criticize her primary rivals by name, often telling reporters, "I'm not here to criticize other Democrats." So her decision to call Bloomberg out in Thursday's speech could mark another sign that her campaign is shifting to a more aggressive strategy less than two months out from the Iowa caucuses.

Addressing Medicare for All

Perhaps more than anything else, it was her pledge at the first primary debate in June that she was all-in on Sanders' "Medicare for All" bill that has, over time, emerged as Warren's stickiest stumbling block. Warren didn't back away from her platform on Thursday, but she did try to reassure more moderate voters of her plans.

A co-sponsor of Sanders' legislation in the Senate, Warren -- after climbing in the polls throughout the summer -- drew unrelenting questions over how she would pay for the single-payer system. Her refusal to engage directly on whether taxes would go up for the middle class under the proposal might have been as troublesome for her campaign as its eventual decision to offer a plan in which they did not, which drew out skeptics on her left and emboldened those to her right.

By the time Warren ultimately released a pair of plans laying out how she would pay for Medicare for All and what the transition period would look like, it was clear that the drawn-out saga had already taken a toll. Buttigieg, who was vocal in his criticism of Warren and her support for Medicare for All, has gained traction in part at Warren's expense.

On Thursday, even as she sharpened her argument against certain rivals, Warren sounded a note of caution -- and reassurance -- to more moderate voters.

"I know I have to compromise, but that's not where we start," she said, shortly after acknowledging that, as president, she wouldn't be able to enact her agenda with a "magic wand."

But Warren did not back off the substance of her platform, which -- no matter the process that might bring it to pass -- would fundamentally remake American economic life. Spending would go up, but not, as Warren reminded voters, without being paid for by higher and new taxes on the wealthy.

"My health care plan delivers the most financial relief, to the most people, more quickly than any plan by any other candidate," Warren said, before spelling out her early agenda -- an aggressive move to expand coverage that would, she has argued in the past and, again on this occasion, promised would tee her up to pass a full "Medicare for All" bill by the end of her first term.