Former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE stood at center stage Thursday night, leading in the polls and earning the most attention from ABC’s debate moderators and his rivals alike.

But Biden acted less like the front-runner than Sen. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.), the candidate emerging as Biden’s chief rival from the progressive wing of the Democratic Party.

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While many of the other candidates competed for audience attention with practiced zingers and dad jokes, Warren once again set much of the early agenda, defending her "Medicare for All" health care plan and swatting away the few attacks that came her way.

For weeks, the debate seemed to promise a much-anticipated showdown between Biden, who has led polls from the beginning of the race, and Warren, the upstart progressive who is slowly chipping away at his lead.

Tellingly, when Biden was prompted to critique the Medicare for All plan that both Warren and Sen. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.) have made cornerstones of their campaigns, Biden turned to Warren first — even though Sanders is the measure’s prime sponsor in the Senate.

But Biden, in the language of the Senate, barely poked at Warren, whom he called “my distinguished friend, the senator on my left.”

Through the more than two and a half hours that followed, that was the extent of their interaction, less a throw-down than a detente.

Many of the other candidates took direct shots at Biden, including the night’s most aggressive attacks, from former Housing and Urban Development Secretary Julián Castro. Castro both questioned Biden’s mental capacity and his ability to build on the Affordable Care Act.

“I’m fulfilling the legacy of Barack Obama Barack Hussein ObamaDemocrats ramp up pressure on Lieberman to drop out of Georgia Senate race The Hill's Campaign Report: Biden on Trump: 'He'll leave' l GOP laywers brush off Trump's election remarks l Obama's endorsements Trump pledges to make Juneteenth a federal holiday, designate KKK a terrorist group in pitch to Black voters MORE, and you’re not,” Castro said.

“That’ll be a surprise to him,” Biden shot back.

“Come on guys,” businessman Andrew Yang Andrew YangBiden's latest small business outreach is just ... awful Doctor who allegedly assaulted Evelyn Yang arrested on federal charges The Hill's Campaign Report: Biden weighs in on police shootings | Who's moderating the debates | Trump trails in post-convention polls MORE sighed.

Warren, by contrast, was one of four candidates who did not attack one of her onstage rivals. And, reflecting a frustration among some other Democratic campaigns who have failed either to match Warren’s steady rise or to land a jab on her, she was one of the few who was not attacked herself, with the lone exception of Biden’s gentle poke.

Through three rounds of debates, where others have found momentary success in lobbing broadsides at their rivals on stage, Warren has not. She has emerged as the most confident in her own agenda, and the most capable of setting the agenda to which the rest of the field responds.

On Thursday, where Biden consulted his notes and corrected himself, Warren parried skepticism over Medicare for All when a rival or a moderator raised a question. Where Biden studiously obeyed the time limits, Warren barreled through the yellow and red warning signs to land her final points.

Warren still trails Biden in most state and national polls, though many of those surveys show Biden’s advantage narrowing. Where Biden played defense, the other candidates seemed unable or unwilling to take on Warren directly.

That included Sanders, who stands the most to lose to his longtime friend as they both compete for votes among the most progressive set within the Democratic electorate. Sanders routinely turned to Biden, finger waving, nearly shouting. The one time he mentioned Warren, it was to amplify her point about the political power of the gun lobby.

Biden seemed pleased with the chance to contrast himself with Sanders, who began his second bid for president as something of a front-runner himself. Biden said Sanders was misguided for thinking an employer would give employees the savings they would reap from Medicare for All.

“For a socialist, you've got a lot more confidence in corporate America than I do,” Biden quipped.

“Let us be clear, Joe, in the United States of America, we [are] spending twice as much per capita on health care as the Canadians or any other major country on earth,” Sanders said.

“This is America,” Biden responded.

“Yeah, but Americans don't want to pay twice as much as other countries,” Sanders shot back.

Three hours later, when ABC moderators said goodnight, Warren walked off stage, once again unscathed by rivals who barely attempted a shot at the woman who is acting like the front-runner.