In what remains a massive field of candidates, 12 of whom qualified for Tuesday's debate in Westerville, Ohio, Warren and Buttigieg stood out from a pack of others who felt at times like they were fading from view.

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And Buttigieg's sharp elbows were on display more pointedly Tuesday as he took shots at a majority of the other candidates on stage in an effort to capitalize on what Democratic voters almost universally say is one of the sharpest and most eloquent minds in the Democratic field.

Buttigieg's first target was Warren herself, after moderators once again put the Massachusetts senator on the spot over whether her "Medicare for All" proposal would raise taxes on middle class Americans. After Warren repeated the same talking point several times, Buttigieg said she had failed to answer a yes-or-no question.

"Your signature, senator, is to have a plan for everything. Except this," Buttigieg said. "I don't understand why you believe the only way to deliver affordable coverage to everybody is to obliterate private plans."

At times, Sanders, Warren's closest ideological ally on stage, acted as her secret weapon, defending her positions in more succinct ways than she had. Sanders, who has spent two presidential races defending his policies rather than his politics, routinely stepped in between Warren and some of her rivals' most cutting attacks.

Biden, the consummate senator who values the relational aspects of politics, declined to engage with his progressive rivals. Asked whether Warren or Sanders could win a general election, Biden struck a middle course.

"Well I think their vision is attracting a lot of people, and I think a lot of what they have to say is really important," Biden said of Warren and Sanders, before pivoting to his own record. "I'm the only one on this stage that's gotten anything really big done."

"When we think our only choices are between endless war or total isolation, the consequence is the disappearance of U.S. leadership from the world stage, and that makes the entire world a more dangerous place," Buttigieg said.

O'Rourke, who has turned his campaign into a crusade for gun control measures after a mass shooting left more than 20 people dead in his hometown of El Paso, Texas, in August, called Buttigieg a "poll-tested" politician after Buttigieg cast doubt on O'Rourke's buy-back proposal. Buttigieg called O'Rourke naive.

"We cannot wait for purity tests, we just have to get something done," Buttigieg said. "I don't need lessons from you on courage, political or personal."

"I understand that this is hard. But I think as Democrats we are going to succeed when we dream big and fight hard, not when we dream small and quit before we get started," Warren said.

Even in the most heated moments of the debate, the 12 Democrats on stage sought to turn attention back to their common foe, President Trump.

"Russia and Putin understand strength. This president, time and time again, is showing moral weakness," Booker said in a largely harmonious conversation about Trump's decision to pull troops out of Kurdish Syria. "This president is making us less safe. He is partnering with Putin more than he is with [German Chancellor Angela] Merkel and [French President Emmanuel] Macron."