Minnesota Sen. Amy Klobuchar was the most direct in her challenges. But Massachusetts Sen. Elizabeth Warren dinged Buttigieg over his answer on marijuana arrests in South Bend. Former Vice President Joe Biden sharply criticized Sanders' 1990s votes on gun control. Businessman Tom Steyer played his most central role in any debate yet. And entrepreneur Andrew Yang took a shot at Buttigieg.
Here are seven takeaways from the debate:
Rivals' goal: Knock down Pete...
If you didn't know Buttigieg had the momentum in New Hampshire coming into tonight's debate, it was clear in the first few minutes.
Sanders, Biden, Klobuchar, Steyer and Yang all took swings at him within the first 30 minutes of the debate. The former South Bend, Indiana, mayor was the target of attacks over his experience, his take on President Donald Trump's impeachment trial and his lack of much experience in business.
Klobuchar, in particular, challenged Buttigieg over his comments dismissive of Washington experience.
"We have a newcomer in the White House and look where it got us," she said at one point. Later, she took a thinly veiled shot at Buttigieg by noting she is "not a political newcomer with no record."
Still, one of the harshest lines of questioning did not come from a candidate, but from ABC debate moderator Linsey Davis, who challenged Buttigieg on his record in South Bend, especially over arrests for marijuana possession during his tenure as mayor.
Buttigieg struggled to defend himself, saying, "Systemic racism has penetrated to every level of our system and my city was not immune."
When Warren was asked if his answer was substantial, she bluntly said, "No."
These focused attacks on Buttigieg underscored how much of the Democratic field views its top objective as stopping his momentum before New Hampshire's primary on Tuesday. And the questions about South Bend highlight perhaps the biggest obstacle in his path to the Democratic nomination: his lack of support among voters of color, who make up a large and important bloc of the Democratic primary electorate as the race moves past Iowa and New Hampshire.
...and knock down Bernie
Iowa didn't deliver in quite the way Sanders hoped, but he was treated like a front-runner by his rivals on Friday night.
Months ago, Biden praised Sanders for his honesty -- in discussing middle class taxes -- when it came to the question of how to pay for "Medicare for All." But that was when Warren was surging, and Sanders' words were a useful cudgel against her.
Much has changed.
"So how much is it going to cost? If you ask Bernie that -- I'll ask him again tonight -- he says, 'Go figure,' " Biden said, referring to Sanders' recent refusal to offer his own specific estimate.
Biden went on to suggest Sanders would get laughed out of Congress if he arrived there, as president, without more details.
Moderator George Stephanopoulos also confronted Sanders with recent attacks from Trump, who ripped "socialism" in his State of the Union speech and in an ad before the Super Bowl.
Asked why Democrats shouldn't be worried those lines will stick, Sanders hit back at Trump and defended his primary rivals.
"Because Donald Trump lies all the time," he said to applause from the audience. "It doesn't matter what Donald Trump says."
Pressed by Stephanopoulos over the modest turnout in Iowa, where Sanders had been plumping for a progressive explosion, Sanders conceded again that he was disappointed by the numbers.
"I think all of us probably could have done a better job in bringing out our supporters," Sanders said, before pivoting to a more flattering metric. "But if there is a good spot, a good aspect about that campaign, is that young people came out in higher numbers than they did during Obama's historic 2008 campaign. And if that happens nationally, we're going win and defeat Trump."
Klobuchar landed her punches. Will it help this time?
Klobuchar continued to do what's allowed her to become a finalist in a field that started with two dozen candidates, turning in another in a string of strong debate performances.
She landed the punches she came in to deliver: She called Buttigieg's experience into question. She cast doubt on Sanders' electability. And she knocked Steyer for his lack of government experience.
"I think we are not going to be able to out-divide the divider-in-chief," she said of the effect Sanders' ideology could have on Democrats' chances of winning in November. "I think we need someone to head up this ticket that actually brings people with her, instead of shutting them out."
And the senator personally spoke about her family, detailing how she was the "granddaughter of an iron ore miner" and "the daughter of a teacher and a newspaperman."
The reality for Klobuchar, though, is that she has consistently turned in strong debates but hasn't climbed past any of the four candidates who have long made up the field's top tier.
The Minnesota senator invested heavily in Iowa, and while she over-performed where many polls put her by garnering 12.3% of state delegate equivalents with 100% of precinct reporting, she still finished fifth. Her lack of support from black voters is even more acute than Buttigieg's, and she's behind in building infrastructure in Nevada and South Carolina -- which means she's even more dependent on gaining altitude from a strong New Hampshire finish on Tuesday.
This debate may have helped in one key area, though: Money.
There were some nice moments
Amid the aggressive policy debates Friday night, the seven contenders on stage sprinkled in some kind moments.
The crowd cheered when Klobuchar, and then Sanders, mentioned the name of the 2012 Republican presidential nominee, Utah Sen. Mitt Romney -- the lone GOP senator to vote for Trump's removal from office.
When Sanders mentioned that he doesn't get many newspaper endorsements, Klobuchar -- who's picked them up in bunches in recent weeks -- helped him out: "You got the Conway endorsement."
When a moderator quoted Hillary Clinton saying that no one likes Sanders, Klobuchar said, "I like Bernie just fine," and Biden walked over and draped his arm over Sanders' shoulder for a brief hug.
And Buttigieg came to Biden's defense when asked about the political impact of Republicans targeting the former vice president and his son Hunter Biden's actions in Ukraine.
"We're not going to let them change the subject. This is not about Hunter Biden or Vice President Biden or any Biden. This is about an abuse of power by the President," Buttigieg said, while ABC kept a camera focused on Biden, who seemed moved by the answer.
"Look, the vice president and I and all of us are competing but we've got to draw a line here. To be the kind of president, to be the kind of human being, who would seek to turn someone against his own son, who would seek to weaponize a son against his own father, is an unbelievably dishonorable thing that is just one more example of why we as a party have to be completely united" to beat Trump, Buttigieg said.
Biden shows he's still in the mix
The former vice president's weak fourth-place finish in Iowa called into question how a candidate whose calling card is his electability could withstand losing elections.
On Friday night, he showed debate-watchers he was still capable of mixing it up with his rivals -- delivering, and at times shouting, passionate answers.
The subject line of the fundraising email his campaign sent moments after the debate: "I fought like hell tonight."
He lambasted Sanders over votes against gun control measures in the 1990s, highlighting the Vermont senator's support for legislation that made it impossible to pursue civil liability claims against gun manufacturers and his five votes against the Brady handgun violence bill. Sanders said that while his views have changed, he was representing the constituents of his rural state at the time.
"Think of all the thousands and thousands of people" who were killed by gun violence, Biden said to Sanders, "while you were representing your constituency."
Biden even defended what Buttigieg called the "politics of the past" -- turning it into another opportunity to tie himself to former President Barack Obama.
"I don't know what about the past of Barack Obama and Joe Biden was so bad," Biden said. "What is it that he wants to do away with?"
And he produced one of the night's most memorable moments, urging the crowd to give a standing ovation to Lt. Col. Alexander Vindman, the top Ukraine expert at the National Security Council who testified during the impeachment hearings and was ousted by Trump's White House hours earlier Friday.
"I think we should all stand now and give Col. Vindman a show of support," Biden said, throwing his hands above the podium. "Get up there!"
Steyer tries to crash through Biden's firewall
Steyer's strategy on Friday was clear: Continue to make inroads with black voters by taking down Biden, whose support among African Americans has proven resilient.
Steyer called for reparations for African Americans, faulted his opponents for saying "not one word" about race and -- in a direct moment -- demanded the Biden disavow Dick Harpootlian, a prominent supporter in South Carolina, who accused Steyer of buying the endorsement of the chairman of the state's Legislative Black Caucus.
"Anyone who thinks that racism is a thing of the past and not an ongoing problem is not dealing with reality," Steyer said.
The trio of debate moments made clear that Steyer sees his path to becoming a viable contender for the Democratic nomination running through South Carolina.
The billionaire businessman has had strong poll numbers in the state recently. A Fox News poll released in mid-January found Steyer at 15% -- behind Biden but ahead of Sanders, Warren and Buttigieg.
Warren picks her spots -- but mostly sticks to script
Warren seemed to disappear from the debate's hottest moments in the early stages, largely sticking to her script and avoiding confrontations with the other candidates as she tries to make her case as the primary's "unity" candidate.
Over past few days, as the Iowa caucuses spiraled into a historic political fiasco and candidates like Biden, Sanders and Buttigieg exchanged attacks, Warren doubled down on her pitch.
She mostly stayed out of the fray, off and onstage, as she sought to position herself as the one hopeful who can pull a fractured party together. But on a debate stage, where conflict draws attention, she didn't draw much.
Until she seized it.
"I lived in an America in which abortion was illegal. And rich women still got abortions," Warren said, the crowd rapt as she warned that the Supreme Court, like many red states, was on a path to banning or making it near impossible for women to obtain them.
The stakes, she added, were clear -- and "if we are going to protect the people of the United States of America and we are going to protect our rights to have dominion over our bodies, then it's going to mean we can't simply rely on the courts."
Noting that a strong majority of American voters support abortion rights, Warren said the only recourse now was to push "for a congressional solution."
"It is time," she said, "to have a national law to protect the right of a woman's choice."
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