WASHINGTON – It’s an axiom in politics that if you don’t want to get razzed for hanging with rich donors, don’t serve them $900 bottles of wine in a cave.

Maybe that’s a bit of a paraphrase. In any case, Pete Buttigieg – or “wine cave Pete” as rivals dubbed him after a recent Napa fund-raiser – wasn’t about to get ambushed Thursday night.

“Billionaires in wine caves should not pick the next president of the United States,” insisted Sen. Elizabeth Warren, striking the sort of populist tone one expects in a Democratic debate.

“Senator, your net worth is 100 times mine,” he shot back. “I’m literally the only person on this stage who’s not a millionaire or a billionaire. This is the problem with issuing purity tests you yourself cannot pass.”

The Democrats’ sixth primary debate featured a set of seven candidates distilled from a field that topped two dozen in the summer. It was contentious. It gave voters much to ponder as they seek a champion to face Donald Trump, impeached one day earlier.

What do they value most — a fresh face? New ideas? The reassurance of gray hair and decades of experience?

Some takaways:

They’re all gunning for Buttigieg

The boyish 37-year-old mayor of small town South Bend, Ind., is the front-runner in the Iowa caucuses 45 days hence. Even without checking the polls, that was easy enough to infer from the attention lavished on him by far more seasoned candidates on stage.

“I do not sell access to my time.…I don’t meet behind closed doors with big dollar donors,” Warren sniffed as she and Buttigieg went back and forth over the wine cave.

Neither hesitated. Quips flew.

“If you can’t say no to a donor then you have no business running for office,” he shot back.

Sanders chimed in. He’s also shunned high-dollar donors and he managed to simultaneously poke Buttigieg and Joe Biden, the national front-runner, noting that the mayor trailed in the tally of millionaire donors, 44 to 39.

But Sanders consoled him, “I know you’re an energetic guy and a competitive guy.”

Indeed he is. Buttigieg came to play. He held his ground and had obviously prepared to parry the expected attacks. He’s not going anywhere without a fight.

Yang, mesmerizing and offbeat

Asked about young immigrants facing deportation, he went off on a tangent about the need for more women in power, because “if you get too many men alone and leave us alone, we kind of become morons.”

Asked about China, he talked about pro-democracy protesters in Hong Kong, then called for more research in artificial intelligence – the technology behind facial recognition systems used against the protesters — so the U.S. can catch up.

“They’re in the process of leapfrogging us in AI,” he said.

It sounded smart, kind of.

Then there was the part about thorium as a superior fuel for nuclear reactors because unlike uranium, it won’t stick around for 100,000 years “and you can’t make a weapon out of it.”

That definitely sounded smart, but a bit of googling might make you wonder. According to the Bulletin of the Atomic Scientists, thorium isn’t any better, because you have to convert it into uranium to generate electricity.

“I know what you’re thinking, America: How am I still on the stage with them?” he quipped in his closing statement.

No doubt that was on the minds of former housing secretary Julian Castro and Sen. Cory Booker, both relegated to heckling via Twitter.

Where was the diversity?

Indeed, without them, the stage in Los Angeles had twice as many non-white moderators as presidential candidates.

For a party that relies so heavily on black and Hispanic voters, it wasn’t a good look.

“It’s both an honor and disappointment to be the lone candidate on this stage tonight,” Yang said. “I miss Kamala. I miss Cory, though I think Cory will be back.”

Experience counts

It’s Biden’s calling card, and Buttigieg’s Achilles heel.

“I’m running because I’ve been around. Because experience often comes with judgment, and a little bit of wisdom,” asserted Biden, 78, the former vice president.

Rumors have swirled that he would vow to serve just one term. A moderator noted that he would be 82 in four years and asked if he would seek reelection if he wins.

“I’m not willing to commit one way or another. I’m not even elected to one term yet. Let’s see where we are. Let’s see what happens,” he said, smiling as he added: “But it’s a nice thought.”

Biden invoked Trump’s relentless attacks over his son’s work for a Ukrainian gas company, presenting himself as a high road kind of Joe who still wants to find common ground. None of his rivals made mention of the allegations; Democratic voters wouldn’t approve, and in any case few view the allegations as anything but fantasy and deflection.

Compared to eight years as understudy to a president, Buttigieg’s service as a small town mayor continues to rankle rivals eclipsed by his charisma.

Klobuchar went for the jugular.

She hit her fellow Midwesterner for not getting very far in elected office before shooting for the Oval Office.

“You should respect our experience,” she said. “Winning matters. I think a track record of getting things done matters.”

“If you want to talk about the capacity to win by putting together a coalition to bring you back to office with 80% as a gay dude in Mike Pence’s Indiana,” he responded.

Not good enough, Klobuchar shot back, noting that he lost his only statewide race by 20 points.

Go bold?

Warren remains the idea factory, and as at previous debates, her plan to slap an annual 2% tax on wealth over $50 million was a touchstone. A moderator noted that many economists warn that her plan would drag down growth.

“They’re just wrong,” she said.

Buttigieg needled Warren at one point over a call for free college for everyone. No, he said, the wealthiest 10%, at least, can afford tuition, and those tax dollars can be used for other priorities.

“We’ve got to break out of the Washington mindset that measures the bigness of an idea by how many trillions of dollars it adds to the budget, or the boldness of an idea by how many fellow Americans it can antagonize,” he said.

It was one of the more elegant lines of the night, and it captured a central tension in the field

Gender gap

The two women on stage were scrappy and assertive throughout the night. More than some of their male rivals. But more than any debate so far, gender difference yawned.

At one point Sanders demanded a rebuttal on the basis of being mentioned by name. When that didn’t work, he feigned emotional distress, insisting that he deserved a turn to talk because a rival had hurt his feelings.

Warren and Sanders didn’t feign. Both choked up, eyes glistening, when candidates were each given the option – in the spirit of the holidays – to offer others a gift, or to ask their forgiveness.

Several men offered copies of books they’d written. The women were the only ones who didn’t pick gift-giving, conceding they’d probably bruised some feelings along the way.

“I will ask for forgiveness. I know that sometimes I get really worked up. And sometimes like that will hot. I don’t really mean to,” Warren said.

“I’d ask for forgiveness, anytime any of you get mad at me. I can be blunt. But I am doing this because I think it is so important to pick the right candidate here, I do,” Klobuchar said.