Every few months a new candidate is discovered by voters, often by a big debate moment or a surge of media appearances. Interest spikes. Polls shift. In no time, the bright and shiny new candidate is roughed up by his or her opponents. Democratic voters, who have consistently told pollsters all year that they are searching for the most electable Democrat, start to have misgivings and they soon abandon the candidate.

The political scientists Lynn Vavreck and John Sides looked at this dynamic in the 2012 Republican presidential primary. That contest had a series of short-lived frontrunners who briefly overtook Mitt Romney before GOP voters returned to him and gave him the nomination. Vavreck and Sides have described that cycle as “discovery, scrutiny and decline”: An interesting new candidate is discovered, followed by an intense phase of scrutiny by the press and his or her opponents. If they don’t survive the vetting, the decline begins.

Buttigieg has clearly been discovered. Thursday night he moved more obviously into the scrutiny phase, with withering criticism from Elizabeth Warren, who is looking to be rediscovered, and Amy Klobuchar, who is looking for a shot at entering the cycle herself.

Before the Pete pile-on occurred, the PBS NewsHour/POLITICO debate at Loyola Marymount University was characterized by a policy-heavy first half devoted to a series of issues that hadn’t received much attention in the previous five Democratic debates.

A lively discussion about whether the existential threat of climate change meant that Democrats should embrace the expanded use of nuclear power, as is common among our European allies, revealed some telling divides. Elizabeth Warren, despite proposing aggressive carbon reduction targets that some scientists do not believe are possible without a full range of alternative energy options, said she wouldn’t shutter currently operating nuclear plants but that she doesn’t favor expansion. Andrew Yang, who wore, as he often does, a pin that said “MATH”, argued that nuclear expansion was essential to solving the climate crisis.

On foreign policy, we learned that Bernie Sanders thinks Bibi Netanyahu is “a racist,” that Warren would recommit to closing the American prison at Guantanamo Bay (though she didn’t say how), that Biden would seek United Nations approval of international sanctions against China, and that Buttigieg would consider a boycott of the 2022 Olympics in Beijing over China’s widespread mistreatment of Muslim Uighurs in western China.

For the first time in a debate, Biden also made a forceful case for how he was right and Barack Obama was wrong on a big policy issue — the surge in Afghanistan — though he didn’t mention the former president by name.

Just when things seemed a tad slow, moderator Tim Alberta, POLITICO’s chief political correspondent, kicked off the highly charged second half of the debate with a provocation.

“Candidates,” Alberta said, “let's make things interesting.”

There were a series of clashes between candidate pairs vying for similar slices of the Democratic electorate. Sanders and Biden, who both draw heavily from white working class voters, had another round of arguing over health care.

Inside the hall, there was a notable dynamic that is not seen on television. Several candidates shoot their hands in the air and stare at the moderators in order to get noticed. Biden had a less-is-more strategy. He rarely raised his hand. Sometimes he stood a step back from the podium with his arms folded, staring around and seeming a bit disengaged and looking for opportunities to speak only when it really mattered.

Warren, on the other hand, gestured toward the moderators almost continuously.

After a long period when candidates frequently didn’t respect the agreed upon rules about interruptions, Biden suddenly exploded at the chance to discuss Medicare for All, the issue that has vexed Warren.

“My name was mentioned,” he roared after Sanders spoke about saving middle class Americans the money they now spend on premiums. “I'm the only guy who has not interrupted. I'm going to interrupt now. It cost $30 trillion. Let's get that straight: $30 trillion over 10 years. Some say it costs $20 trillion.” He pointed towards Warren.

"Some say it costs 40,” he went on. “The idea that you're going to be able to save that person making $60,000 a year on Medicare for All is absolutely preposterous.”

But the two sharpest attacks of the night were reserved for Buttigieg.

Elizabeth Warren mocked the young mayor for his recent fundraiser held in northern California.

“So the mayor just recently had a fundraiser that was held in a wine cave full of crystals and served $900 a bottle wine,” she said, accurately. “Think about who comes to that. He had promised that every fundraiser 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.”

Klobuchar soon jumped into with her own wine cave dig. “I have never even been to a wine cave," she said, perhaps speaking for most viewers. Even Yang, who has never to my recollection attacked an opponent on stage at a debate, threw a wine cave elbow, pointing out that his Freedom Dividend would give voters extra money they could use to support candidates, “because they don't have to shake the money tree in the wine cave.”

Buttigieg’s response to Warren was well prepared. He accused her of enacting “purity tests you cannot yourself pass,” noting that she was wealthier than Buttigieg and in fact that it wasn’t long ago that she was holding the same kind of high dollar fundraisers — and even transferred millions of dollars raised that way into her presidential campaign account.

Buttigieg cleverly framed taking money from his wine cave patrons as necessary because Democrats need everything to defeat Trump.

Klobuchar, who had one of the finest and most confident performances of the night, practically rolled her eyes at Buttigieg as she dryly went through his thin resume.

“I know you ran to be chair of the Democratic National Committee,” she said. “That's not something I wanted to do. I want to be president of the United States. And the point is, we should have someone heading up this ticket that has actually won.”

Buttigieg responded with a slightly weak plea about how he won his mayor’s race with 80% of the vote, though he didn’t point out that that represented a total of 8,515 votes in South Bend.

Klobuchar was unimpressed.

“Again,” she said dryly, referring to his failed bid for state treasurer, “If you had won in Indiana, that would be one thing. You tried and you lost by 20 points.”

