(CNN)Former Vice President Joe Biden had a tongue-in-cheek plea for Sen. Kamala Harris at the start of Wednesday's debate: "Go easy on me, kid."
But his chief antagonist and other top rivals did exactly the opposite on a night of political bloodletting that turned into the most negative moment yet in the Democratic presidential race -- and likely delighted Donald Trump.
The second night of a debate double header turned into a bruising slog as marquee candidates filleted one another's records and struggled to train a concentrated and effective attack on Trump -- an obvious target given the fierce Democratic antipathy to his presidency.
Biden, Harris and New Jersey Sen. Cory Booker especially all absorbed attacks that could be exploited by Trump down the road.
Despite the punches thrown in Detroit on Wednesday, the debate did not appear to bring the party closer to the goal that unites all Democrats -- ejecting Trump from the Oval Office.
After both encounters this week, the most vexing questions for Democrats remained whether their expansive bench of candidates contains any single one with the dexterity and toughness to take on the storm that awaits from Trump in the head-to-head presidential debates in fall 2020.
"You want to be president of the United States, you need to be able to answer the tough questions," New York Mayor Bill de Blasio told Biden during one tough exchange.
"I guarantee you, if you're debating Donald Trump, he's not going to let you off the hook."
On Tuesday, a first debate featuring big hitters like Sens. Elizabeth Warren and Bernie Sanders reverberated with policy give-and-take, political substance and a sense of freshness that suggested a party with a mission. Wednesday's encounter was more bitter in tone, resonating with personal animus. Ill feeling between Biden and Harris, left over from their bruising first encounter in July, intensified.
The former vice president did what he needed to do -- he survived after a disastrous first debate performance last month. But it is still unclear whether he is a genuine front-runner with the juice to ride his lead all the way to the nomination or could begin to fade when first primary and caucus votes are cast.
Harris had trouble living up to an electric debut in the first debate and sometimes struggled to combat attacks on her recently released health care plan and past confusing statements on the issue.
The Californian faced a particularly sharp assault from Hawaii Rep. Tulsi Gabbard on her record as a prosecutor but shrugged it off as an inevitable sign of her own success.
"This is going to sound immodest, but I am obviously a top tier candidate, so I did expect I would be on the stage and take hits tonight," Harris told CNN's Anderson Cooper, slamming Gabbard as "an apologist" for Syrian leader Bashar al-Assad.
As the dust settles, Booker, who was the most sprightly and unifying candidate on stage, may come to be seen as the big winner -- but with a caveat as he had to stand by as Biden prosecuted an attack over his record as mayor of Newark.
The feuding intensified as outsider candidates, desperately needing a moment before qualification criteria tightens for future debates teed off on potential eventual nominees.
"We have got to get ready for a fall campaign and it's gotten a little nasty, and a lot of the things we hear tonight could come back and hurt us when we finally run against Donald Trump," former Virginia Gov. and CNN commentator Terry McAuliffe said.
No killer blows
All early debates represent the first engagements in a long political war. Candidates tend to improve through election season, so Wednesday's missteps can be repaired. When the field narrows, the debates will become more cohesive and may train a more effective critique on Trump.
And good campaigns and candidates learn how to repel attacks revealed in primary debates. So the wounds inflicted on half of the Democratic field on Wednesday may not be decisive.
And the general election could become a referendum on Trump's presidency -- for all his threatening political and presentational skills -- which may give Democrats an advantage given the President's unpopularity.
For all the sparring, no candidate appeared to land a killer blow or to lift themselves above their rivals on the stage. What was missing was a candidate who could synthesize a set of detailed policy plans, infuse their candidacy with a soaring sense of mission and wrap it all up in a coherent critique of a President who has never cracked 50 % in job approval polls and is using racism as a political tool.
Biden survives but fails to dominate
The big question going into the debate was whether Biden, who stumbled badly in the first encounter in June, could bounce back and dominate the stage as he currently does polls of the Democratic race.
The former vice president was undeniably more engaged and energetic than he was in the first debate. And his front-runner spot in the middle of the stage was riddled with crossfire.
Harris clashed heatedly with Biden on health care and abortion
"Under your plan, status quo, you do nothing to hold the insurance companies to task for what they have been doing to American families," Harris told Biden.
Booker upbraided Biden on his record on criminal justice.
"You are dipping into the Kool-Aid and you don't even know the flavor," Booker charged.
Former Housing and Urban Development Secretary Julian Castro upbraided him on immigration.
"It looks like one of us has learned the lessons of the past and one of us hasn't," Castro told Biden, whose near half century long record in Washington is one of his biggest political liabilities.
New York Sen. Kirsten Gillibrand even questioned whether Biden wanted women to work outside the home.
The former vice president held his ground in most of the attacks, did not make huge errors and did nothing to torpedo his own campaign. And that none of the other candidates on stage turned in a dominant performance also helped him.
But it took what seemed like ages for him to unveil his most potent weapon -- the eight years he spent as right-hand man to the most recent Democratic president who remains hugely popular among the party's voters.
"Everybody is talking about how terrible I am on these issues," Biden said. "Barack Obama knew who I was."
Yet the 76-year-old wasn't sufficiently nimble to dispel questions about his age that are going to follow him all the way until November 2020 since he would be the oldest president inaugurated for a first term.
And Biden appeared less successful in making the point that less well-known moderates made on Tuesday night that the progressive policies of candidates like Warren and Sanders could take the party way to the left of independent voters who the party needs to win the election.
He also noticeably stumbled on a few answers and found it hard to pivot from defending himself against the incessant attacks to his central campaign message -- that he is the best prepared and politically suited candidate to take down Trump.
Critics might argue that focusing on Biden's optics distracts from the profound policy debate that Democrats want to hear. But he is running for the world's most demanding job at an advanced age and set up the comparison by presenting himself as the only candidate with the tools to face down Trump.
