One of the key takeaway tension moments getting talked about from Thursday night's Democratic candidate debate was one in which Senator Elizabeth Warren called out Mayor Pete Buttigieg for attending a recent fundraiser hosted by billionaires, with "$900 bottles of wine" in a wine cave.

Buttigieg quickly retorted that such "purity tests" among candidates were disingenuous, even suggesting that Warren herself couldn't pass the same test, in terms of accepting money from well-heeled donors. But the damage, temporary or not, was done. And Warren's barb was based on an Associated Press story published last Friday that shared details of a Buttigieg fundraising dinner that was held on Sunday, December 15 in the Hall Rutherford wine caves in Napa — one of several private fundraising stops Buttigieg made in the Bay Area in the last two weeks.

As the story detailed, the wine cave in question, owned by billionaire Democratic donors Craig and Kathryn Hall, boasts a Swarovski crystal chandelier with 1,500 crystals. Also, Hall Wines is among the many Napa wineries producing pricy Cabernet Sauvignon that's marked up based on the Napa name, and while a 2016 Montagna Vineyards Cab will run you $250, and a 2014 Kathryn Hall Cab magnum is listed on the website for $450, the AP reporter apparently latched onto some of the pricier estate bottles the winery doesn't currently have for sale.

"The mayor just recently had a fundraiser that was held in a wine cave full of crystals with $900-a-bottle wine," Warren said during the debate. "He had promised that every fund-raiser he would do would be open-door, but this one was closed-door. We made the decision many years ago that rich people in smoke-filled rooms would not pick the next president of the United States. Billionaires in wine caves should not pick the next president of the United States."

Buttigieg looked as visibly uncomfortable — and attacked — as he has during any of the Democratic debates this year as Warren singled him out. And his defense was predictably defensive: "You know, according to Forbes magazine, I’m literally the only person on this stage who is not a millionaire or a billionaire. So this is important. This is the problem with issuing purity tests you cannot yourself pass. If I pledge — if I pledge never to be in the company of a progressive Democratic donor, I couldn’t be up here. Senator, your net worth is 100 times mine. Now, supposing you went home and felt the holiday spirit — I know this isn’t likely, but stay with me — and decided to go on pete.com and gave the maximum allowable by law, $2,800, would that pollute my campaign because it came from a wealthy person?"

Buttigieg, like any of the prominent Democratic hopefuls, will of course end up in bed with the liberal wealthy of California and elsewhere, but this was Senator Warren trying to get an edge in the Iowa caucuses, where such things will obviously play to her advantage.

Attacks on Buttigieg were expected at Thursday's debate after polls have showed him surging ahead of the more seasoned candidates, Warren, Senator Bernie Sanders, and Vice President Joe Biden, in Iowa polls. In this case, Buttigieg implied in his further responses to Warren that this angle of attack — implying that wealthy donors corrupt a candidate — was false, and that Obama couldn't have been elected without such donors, as the New York Times noted.

In a related story, the same AP reporter who broke the story, Brian Slodysko, reported that Trump's D.C. hotel is raking in suspiciously high room rates — some as high as $6,719 per night — ahead of a private fundraising event last weekend.

As the AP reported on the Buttigieg fundraiser, the Halls are "prolific donors who split their time between Dallas and their California wineries." But they are part of a wealth establishment that more seasoned candidates may want to distance themselves from. Kathryn Hall landed an ambassadorship in Austria, seemingly as a result of the couple's donations to the Clintons in the 1990s. And Craig Hall was chairman and founder of the Hall Group, which got a controversial $300+ million government bailout during the savings and loan crisis in the 1980s.

Warren said during the debate, "I don’t meet behind closed doors with big-dollar donors. Look, I have taken one that ought to be an easy step for anyone here. I said to anyone who wants to donate to me, if you want to donate to me, that’s fine. But don’t come around later expecting to be named ambassador, because that’s what goes on in these high-dollar fund-raisers. I said no, and I asked everybody on this stage to join me. This ought to be an easy step. And here’s the problem. If you can’t stand up and take the steps that are relatively easy, can’t stand up to the wealthy and well connected when it is relatively easy, when you are a candidate, then how can the American people believe you will stand up to the wealthy and well connected when you are president and it is really hard?"

Both Sanders and Warren campaign strategist seem to think the AP story, about the previously undisclosed fundraiser, was gift.