“You’re not going to out-left Bernie Sanders and Elizabeth Warren,” said Mathew Littman, a Democratic strategist and former Biden speechwriter who now supports Kamala Harris. “But you could be the new moderate voice in the race.”

The new strategy for lower-polling candidates was laid bare in their bloodlust for Warren on Tuesday. In part, the pile-on reflected the execution of traditional debate stagecraft: conflict generates coverage, and a candidate who isn’t involved gets forgotten.

But for moderate Democrats, a more revealing calculation was also at play — that if Biden implodes, the candidate who most sharply contrasts with Warren will be best positioned to pick up the pieces and take Biden’s place in the race.

“That’s exactly it,” said an adviser to one candidate, suggesting an offensive that is likely to animate the next month of the campaign.

The assault against the progressive twin towers began almost as soon as the debate started and carried over in the next day, as Democrats zeroed in on Warren for ducking a question about whether enacting Medicare for All would require a tax increase on middle-class Americans.

“There’s still been no explanation for a multi-trillion dollar hole in this plan,” Buttigieg, the mayor of South Bend, Ind., said on CNN on Wednesday. “I have a lot of respect for Senator Warren, but last night she was more specific and forthcoming about the number of selfies she’s taken than about how this plan is going to be funded.”

During the debate, Klobuchar and Beto O’Rourke, the former congressman from Texas, all but accused Warren of engaging in class warfare, while Klobuchar offered a “reality check” on her proposals.

"The difference between a plan and a pipe dream is something that you can actually get done,” Klobuchar, the Minnesota senator, said.

Paul Maslin, a top Democratic pollster, said Buttigieg and Klobuchar “finally got to the place where they can best articulate, ‘We don’t have to go to the extreme.’ … Having said that, I think Bernie [Sanders] and Warren were both pretty effective in the way they countered it.”

The result, Maslin said, is that “you started to see the lines being drawn more clearly” in the campaign, with the electorate witnessing a “substantive … fair test” of ideas.

For Biden’s progressive rivals in the top tier, Sanders and Warren, the former vice president is still ripe for takedowns. Warren snubbed Biden during a conversation about the creation of the Consumer Financial Protection Bureau, when Biden said he “went on the floor and got you votes.”

Warren responded, “I am deeply grateful to President Obama, who fought so hard to make sure that agency was passed into law.”

And Sanders responded to Biden’s claim that he was the only candidate who “has gotten anything really big done,” by saying, "But you know what you also got done — and I say this as a good friend — you got the disastrous war in Iraq done.”

Yet lower-polling moderates — the candidates who stand to gain the most from a Biden crash — largely laid off him. Biden continues to poll well nationally, and direct efforts by his rivals in previous debates to dislodge him fell flat.

If he is softening, it is because he has fallen behind Warren in some critical early state polls — and because money is running thin. Biden ended September with about $9 million on hand, far less than Warren, Sanders and Buttigieg.

“It kind of seems like Biden’s collapsing under the weight of his own operation,” said Colin Strother, a veteran Democratic strategist.

Biden’s rivals, he said, are making him “dig his own way out.”

On Tuesday, Biden’s opponents did just that. They let him off the hook when he declined to directly answer a question about why it was appropriate for his son to engage in business in Ukraine while Biden was vice president.

“My son did nothing wrong. I did nothing wrong,” Biden said, before pivoting to Trump.

Sen. Cory Booker — who directly attacked Biden in earlier debates — even took pains to defend the former vice president, scolding the debate moderators for even bringing Biden’s son up.

“We are literally using Donald Trump’s lies,” Booker said. “And the second issue we cover on this stage is elevating a lie and attacking a statesman. That was so offensive.”

Michael Ceraso, a former New Hampshire director for Buttigieg’s presidential campaign, said that before Tuesday, the narrative surrounding the primary consisted almost exclusively of Biden and Warren.

“Now,” he said, “I feel like it’s Pete, Klobuchar trying to get in the same breath as Warren — that there’s an alternative.”

In criticizing Warren, candidates such as Buttigieg and Harris could potentially cut into her support among women and Democrats with postgraduate degrees. And in a contest in which many Democrats remain undecided — and not motivated principally by ideology — any number of lower-tier contenders believe they can make late-2019 gains.

But there is risk in pushing hard from the center. Together, Warren and Sanders account for about 40 percent of Democrats’ national primary support, according to the latest Morning Consult survey. And it wasn’t only moderate Democrats who appeared likely to help their cause this week. In his first debate following his heart attack, Sanders did, too.

He gently challenged Warren on taxes, prompting Klobuchar to say that “at least Bernie’s being honest here.” In addition to his $33.7 million cash on hand, Rep. Alexandria Ocasio-Cortez plans to endorse him on Saturday.

“I think the challenge for the lower-polling moderates is that they’re misjudging where the Democratic electorate is,” said Andrew Feldman, a Democratic strategist. “It doesn’t seem like the Democratic electorate at this point wants a run-of-the-mill moderate. Joe Biden is not a run-of-the-mill moderate because of his personal connection to voters through his Obama legacy. And Mayor Pete is a moderate, but he is a generational alternative to Biden.”

Feldman added, “Everyone else essentially is just trying to break through.”