In the sixth Democratic debate, a question about whether women make better leaders than men turned into a heated back-and-forth between Sen. Elizabeth Warren (D-Mass.) and South Bend, Ind., Mayor Pete Buttigieg over the role of money — and wealthy people — in politics.

The moment allowed frequent allies Warren and Sen. Bernie Sanders (I-Vt.) to try to attack Buttigieg in the weeks before the first votes are cast, on Feb. 3 in Iowa, where Buttigieg is basically tied with the two of them and former vice president Joe Biden, according to a Washington Post average of polls. And it showcased a growing debate in the Democratic Party about whether wealth corrupts.

What happened

Politico’s Tim Alberta said: “Former president Obama said this week when asked who should be running countries, that if women were in charge, you’d see a significant improvement on just about everything. He also said, ‘If you look at the world and look at the problems, it’s usually old people, usually old men not getting out of the way.’ ” He asked Sanders to respond.

Sanders quipped: “And I’m white as well.” He said he respectfully disagreed with Obama but quickly pivoted to his central talking point about income inequality. “The issue is where power resides in America. And it’s not white or black or male or female. We are living in a nation increasingly becoming an oligarchy, where you have a handful of billionaires who spend hundreds of millions of dollars buying elections and politicians.”

When it was Warren’s turn, she held up her campaign’s strategy of taking selfies with anyone who wants one at a rally as an example of walking the walk of reaching out to everyone.

“I made the decision when I decided to run not to do business as usual. And now I’m proud of the 100,000 selfies [I’ve taken]. … Most of the people on the stage run a traditional campaign, and that means going back and forth from coast to coast to rich people and people who can put up 5,000 bucks or more in order to have a picture taken, in order to have a conversation and in order maybe to be considered to be an ambassador.”

When she finished, Buttigieg responded:I can’t help but feel that might have been directed at me.” Warren has been criticizing his fundraising from high-dollar donors to draw a contrast with how she and Sanders take a less-traditional approach of courting lots of small-dollar donors.

Buttigieg defended his fundraising: “The way we’re going to win is to bring everybody to our side in this fight. If that means that you’re a grad student digging deep to go online to peteforamerica.com and chip in 10 bucks, that’s great. And if you can drop a thousand dollars without blinking, that’s great, too. We need everybody’s help in this fight. I’m not going to turn away anyone who wants to help us defeat Donald Trump.”

Warren brought up that he recently held a fundraiser at a Swarovski-crystal-decorated winery. “Billionaires in wine caves should not pick the next president of the United States,” she said.

Buttigieg shot back, saying that according to Forbes, he’s “literally the only person on this stage who is not a millionaire or a billionaire. So this is the problem with issuing purity tests you cannot yourself pass.”

After they went back and forth a few rounds, Buttigieg pointed out that Warren has transferred money from her Senate campaign, in which she did hold closed-door fundraisers, to her presidential campaign. He accused her of denouncing “the same kind of fundraising guidelines that President Obama went by, that Speaker Pelosi goes by, that you yourself went by until not long ago in order to build the Democratic Party.”

Warren did not have a chance to respond as other candidates started chiming in.

The backstory

Candidates divide their donors into two groups: small (those who donate $200 or less) and large (those who donate more than $200). Large-dollar donors are obviously more fruitful, because you get more money per person, though small-dollar donors are easier to reach with a click of a button, via email or an online ad. Big donors often give in fundraisers, like the one at that winery Buttigieg visited.

But as the Democratic Party has taken a more populist tone, fundraising from the “average American,” who contributes $25 or so, has become a politically valuable thing to tout, implying that the candidate is not in the pocket of big donors and their interests. No candidates have led this charge more so than Sanders and Warren, who have said they won’t take money from closed-door fundraisers.

They can afford to do that because their national profiles are high. Sanders in particular has a large and devoted following sprawled out across the nation that he has built into a successful online fundraising infrastructure.

Warren has said she will accept money from millionaires but that she won’t seek them out in private fundraisers. She’s tried to highlight that with a pledge not to make donors ambassadors, a post that can be awarded to a president’s highest donors. Buttigieg has said he won’t sign on to that.

As Buttigieg has risen in the polls, Warren in particular has taken aim at his more traditional way of fundraising. She suggested he is “beholden” to wealthy donors. Buttigieg pushed back on that vehemently. If “doing traditional fundraisers disqualifies you from running for president, I guess neither one of us would be here,” he said at a recent Washington Post Live event.

Each has attacked the other’s disclosures — on campaign finance and donors — in part to point to places where they believe the other candidate isn’t being fully forthcoming with voters.

As Warren kept up her attacks, Buttigieg announced recently he would open his fundraisers to journalists in an effort to be more transparent about where his campaign gets its money. The Post has reported that since September, less than half of his campaign money has been from small-dollar donors.

Warren and Buttigieg wouldn’t be attacking each other on fundraising and transparency if they didn’t see each other as threats. Expect to hear much more about this leading up to the first votes in February.