A younger candidate complained that the old guard wasn’t moving fast enough. An older candidate shot back that the next generation should wait its turn. There was shouting on stage, and that was exactly the moment Kamala Harris wanted.

“Hey, guys -- you know what,” the California senator said, jumping in with an apparently calculated mix of authority and light-hearted exasperation, “America does not want to witness a food fight. They want to know how we're going to put food on their table.”

Judging by the applause, this peace-keeping appeal was a winner, and for a while intra-party attacks were infrequent as Democratic candidates focused more on pitching themselves as the anti-Trump champion-to-be than on hitting each other over ideology or personality.

But that was at the second debate in Miami, way back in June. Ahead of the latest round tonight in Westerville, Ohio, discord has resurfaced and the knives are very much out.

This fight started over assault rifles, but it has more to do with candidates jockeying for survival. “I heard some of the comments made today on this stage,” Beto O’Rourke said Oct. 2 at a March for Our Lives forum in Las Vegas. “Those who are worried about the polls and want to triangulate — I’m thinking about Mayor Pete on this one.”

The remark’s impact seemed to fizzle out in the moment, but two weeks later the mayor of South Bend, Ind., responded to his rival, who’s polling at 2.6% support in the RealClearPolitics average.

“I get it,” Buttigieg told Snapchat’s Peter Hamby on Monday. “He needs to pick a fight in order to stay relevant.”

Then, sensing vulnerability in the mayor tied for fourth place, opponents quickly piled on.

“Leaving more than 5 million assault weapons on the street isn't a ban, it's a Band-Aid,” Harris tweeted in response to Buttigieg, who had called the mandatory gun buybacks that O’Rourke supports “confiscation.”

Cory Booker, who all but admitted earlier in the month that his campaign is running on fumes, jumped in. “Calling buyback programs ‘confiscation’ is doing the NRA's work for them,” the New Jersey senator (polling at just 1.6% tweeted) “and they don’t need our help.”

That Booker and Harris would attack Buttigieg is not surprising. Both were considered heavyweights and carried the hopes of their party with them before the primary began, notably from their perches on the Senate Judiciary Committee where they went to war with Supreme Court nominee Brett Kavanaugh. Those parliamentary fireworks have not fueled polling success, however, and the two are desperate for a breakout moment.

If given a chance, the three will likely renew those attacks against Buttigieg in prime time. That is, if a bigger fight doesn’t sidetrack that skirmish. The Midwestern mayor is going hard after Elizabeth Warren.

The Massachusetts Democrat reversed course recently, promising she could win the White House without big money donors if given the nomination. The good-government overture was well received: Warren raised $24.6 million in the last fundraising quarter and sits at second place in the RealClearPolitics average at 23.4%.

Buttigieg wrote it off as a gimmick, telling Snapchat, “We're not going to beat Trump with pocket change.” To defeat an incumbent -- and a GOP machine -- with $125 million in the bank from the last quarter alone, the mayor argued, small donations will not be enough. Warren did not respond. She didn’t need to as others progressives swarmed in her defense.

“Small-dollar grassroots campaigns, aka what Buttigieg insults here as ‘pocket change,' out-fundraise him by millions,” New York Rep. Alexandria Ocasio-Cortez clapped back on Twitter. “Our nation’s leaders should be working to end the era of big money politics, not protect it. [And] Beto’s gun policy isn’t ‘picking a fight,' it’s taking a stand.”

Either the assault weapons fight or the money fight could spill into a real-time melee on the Ohio debate stage with Buttigieg in the middle. Anything could happen, but one thing is certain: The easy-going part of the Democratic race is over. Earlier, only long shots threw elbows frequently and dropped out subsequently (save for Rep. Tulsi Gabbard, who belatedly earned a spot among the dozen squaring off). Now, almost half of the field is launching attacks, and the Grand Old Party is surely reveling in the discord.

The Trump campaign has long bet that the Democratic primary would turn into a Thunderdome where dozens of candidates enter, and one bloodied winner exits to limp toward the starting line of the general election. But not all Democrats are interrupting their debate prep with broadsides.

Former Vice President Joe Biden had kind words in Iowa for Buttigieg.

“I’m a friend of Pete Buttigieg,” the front-runner said at a presidential forum on Sunday after his fellow candidate left the stage. “By the way, he’s a really decent guy. I turned on the television this morning and he was defending my family against these outrageous, lying ads of the president of the United States of America. That’s a good man.”

Was Biden’s remark calculated? Perhaps. Given the hubbub surrounding his son Hunter’s business dealings in Ukraine and China, soliciting some goodwill ahead of the debate would seem to be sound strategy.