CONCORD, N.H. — Sen. Elizabeth Warren, D-Mass., is ramping up her criticism of one particular Democratic rival — former South Bend, Indiana, Mayor Pete Buttigieg — ahead of a make-or-break primary in which many voters are torn between the two.

It comes at a time when other Democratic rivals are also taking one of the newly minted front-runners to task. Warren is doing so as she pitches herself as the only candidate who can unite the Democratic Party.

Like Sen. Bernie Sanders, I-Vt., Warren has centered her criticism of Buttigieg on his having accepted campaign donations from a series of billionaires. The issue came up during Friday's Democratic primary debate in Manchester, and Warren has revisited it multiple times in the days since.

Asked about the coalition Buttigieg seeks to build, Warren said Sunday on ABC's "This Week" that "the coalition of billionaires is not exactly what's going carry us over the top."

"Here's the thing," she said. "If it's going to take sucking up to billionaires or being a billionaire to get the Democratic nomination to run for president, then all I can say is buckle up, America, because our government is going to work even better for billionaires and even worse for everyone else."

It's an on-brand criticism from a candidate who has pitched herself as an anti-corruption crusader looking to ferret big money out of the political process and hit the country's ultra-rich with a wealth tax.

Speaking at Saturday's McIntyre-Shaheen dinner in Manchester — where Warren and Buttigieg had the two largest cheering sections — Warren said it's "not a time to nibble around the edges of problems" or to "be vague and elusive" with policy prescriptions. She added that she is "not running a race that has been shaped by a bunch of consultants. I'm not offering a bunch of proposals that have been carefully designed not to offend big donors."

"I passed that stop sign a long time ago," she added.

Standing next to a large banner reading "The Best President Money Can't Buy" during a rally in Concord on Sunday, Warren echoed those lines, saying it was "no time for small ideas." Speaking to reporters after the event, she said she "didn't pick out a bunch of proposals that were designed not to offend big-dollar donors."

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Buttigieg has repeatedly hit back at the similar criticism lobbed by Warren and Sanders. Speaking on CNN's "State of the Union," Buttigieg said the election "is about making sure we bring everybody into the fight at a moment when we're going to be going up against Donald Trump, who with his allies are raising — I think the other day they raised 25 million bucks in one day."

"This is the fight of our lives," he said. "I'm not a fan of the current campaign finance system, but I'm also insistent that we've got to go into this with all of the support we can get."

On "Fox News Sunday," Buttigieg said he is "building a campaign that's not defined by who we reject."

"It's defined by belonging. It's defined by inclusion. It's defined by pulling together the coalition to get the job done," he said. "And at the end of the day, whether somebody goes to peteforamerica.com and chips in 5 bucks ... or whether somebody comes to an event and [is] maybe a surgeon who can contribute $2,000 without it being much skin off their back, I want all of them to be part of this effort."

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The dust-up came as Buttigieg claimed victory in Iowa, where Warren finished third. Buttigieg is polling second in New Hampshire, behind Sanders, while Warren finds herself third, according to the RealClearPolitics average of several polls.

Buttigieg and Warren have significant overlapping support from Democrats who may be less ideologically driven but want an erudite nominee. Surveys indicate that both candidates appeal to educated and upscale voters — unlike Sanders and former Vice President Joe Biden, who are stronger with lower-income voters.

John Onoroski of Hudson said at a Buttigieg rally in Nashua that he plans to vote for Warren but that Buttigieg is his second choice.

"She's a progressive, and so am I," he said. "But she's actually managed to get things done, like the Consumer Financial Protection Bureau. I don't think Pete's going to change much if he gets to Washington."

Ty Steinhauser, who's based in New York, said that he's undecided but that Buttigieg and Warren are at the top of his short list.

"I kind of debate between the two of them," he said after attending Buttigieg's town hall Sunday in Nashua. "Pete, I think, is the visionary right now. Warren has actually got stuff done."

While the two are looking to pick up many of the same voters, Warren and Buttigieg offer different tones. Warren appeals to Democrats looking for a fighter who channels their dissatisfaction with the economic status quo and will work to restructure it. Buttigieg is a favorite of many voters who like his calm temperament and would be happy to see incremental and bipartisan change.

At Warren's event in Concord, Sam Sikder, a Warren supporter from Massachusetts, said that while it's noble to criticize the influence of billionaires, the current state of play makes it impossible to eliminate their influence.

"I think that if you look at the candidates, all of them have shady donors," she said. "The amount of money doesn't matter. I know that a lot of people try to do a grassroots campaign, but unfortunately, the political environment requires that they have massive amounts of money now just to compete.

"I think that being conscientious about who is donating to you and what you do with that money is very important," she added. "It needs to be transparent."

For New Hampshire voter Colin Pio, a Warren supporter at her Concord rally, the contrast between candidates' accepting such donations and not accepting them was huge in deciding whom to support. And Warren's stance attracted him to the senator.

"I really want to beat Donald Trump," Warren said Sunday in Newport. "That's my Number 1 job. And I think I'm the best person to beat Donald Trump, and I'll tell you exactly why. We've got to do this. We've got to pull our party together. We cannot have a repeat of 2016. We have got to be a part of this, pull together, and that means we can't be spending all our time attacking each other."