(CNN) -- Pete Buttigieg called it "unwatchable." Amy Klobuchar warned that "a house divided cannot stand." Julián Castro said what was unfolding on stage was "called an election."
Democrats met for their third debate of the 2020 presidential primary Thursday night in Houston. With the field narrowed to just 10 candidates who qualified for the stage, it was messy, and at times nasty.
The night featured Castro launching a series of risky attacks on the front-runner in national polls, former Vice President Joe Biden. It saw fellow Texan Beto O'Rourke have his best moments yet on home-state turf. And it offered another gauge of how the party's raging debate over health care is evolving, with Biden leading the centrist candidates in fighting back more forcefully against "Medicare for All."
Buttigieg, the South Bend, Indiana, mayor, tried at one point to pull Democrats out of the mud.
"This is why presidential debates are becoming unwatchable. Because this reminds everybody of what they cannot stand about Washington. Scoring points against each other, poking at each other, and telling each other that, 'My plan, your plan,'" he said.
That's when Castro, the former Housing and Urban Development secretary and the chief instigator Thursday night, interjected.
"Yeah, that's called the Democratic Primary Election, Pete. That's called an election. That's an election. You know?" he said. "This is what we're here for. It's an election."
Here are seven takeaways from the third Democratic debate:
1. Castro's launches an attack on Biden
Much of the pre-debate hype focused on the potential for an ideological clash between Biden and Massachusetts Sen. Elizabeth Warren, who were sharing the stage for the first time.
But it was Castro, a member of former President Barack Obama's Cabinet, who came ready to brawl with party's front-runner.
Criticizing Obama over deportations, Castro said of Biden: "He wants to get credit for Obama's work, but not have to answer any questions."
"I stand with Barack Obama all eight years, good, bad and indifferent. That's where I stand," Biden responded.
The back-and-forth raised questions about what Obama's legacy really is -- and how Democratic voters want to see it furthered. Do they want to elevate his loyal vice president? Or are they looking for what Obama once was: A young, inspirational candidate to lead them into the future?
It's not clear that Castro qualifies as the latter. His attacks on Biden perhaps weakened Biden but also risked alienating Democratic voters, who largely like all their leading candidates, including the former vice president.
The most stunning of their exchanges was the first one, when Castro launched a very-thinly-veiled assault over a topic other Democrats have only gingerly broached: Biden's age.
He accused the former vice president of "forgetting what you said two minutes ago" during an exchange over whether Biden's health care plan would require Americans who want to sign up for his Medicare-style public option would have to buy into it.
Then, he tried to twist the knife, saying: "I'm fulfilling the legacy of Barack Obama and you are not."
Castro told CNN's Chris Cuomo after the debate that the comment was "not intended as a personal attack or affront."
"This is a debate. And when we're talking about health care policy, we're talking about a policy that impacts every single person in this country," Castro said.
On CNN after the debate, New Jersey Sen. Cory Booker implied Castro had taken a "cheap shot" and said that "tone and tenor are important," even as he also insisted Castro's attacks reflected broader concerns about Biden.
"I think that we are at a tough point right now, because there's a lot of people who are concerned about Joe Biden's ability to carry the ball across the end line without fumbling. And I think that Castro had some really legitimate concerns about, can he be someone in a long, grueling campaign who can get the ball over the line? And he has every right to call that out," Booker said.
There's another possibility to consider. Castro has been a contender for the Democratic vice presidential nomination before. If another candidate on stage Thursday night (other than Biden) wins the nomination and is looking for an attack dog for a running mate, Castro gave them something to think about.
2. Biden vs. Warren and Sanders on health care
Democrats' differences on how to achieve universal health coverage has dominated the opening portions of all three debates. The only difference Thursday night was that all the leading candidates were on stage.
Biden was quick to criticize Warren, who supports Vermont Sen. Bernie Sanders' Medicare for All plan in which private insurance would effectively be ended and all Americans would be enrolled in a government program.
Instead, Biden said, he is offering a more modest proposal that builds on Obamacare by giving Americans the option to buy into a Medicare-style program -- but doesn't require it.
"I know the senator says she is for Bernie," Biden said. "Well, I am for Barack."
Warren attempted to defuse Biden's approach by praising the former president. "We all owe a huge debt to President Obama, who fundamentally transformed health care in America and committed this country to health care for every human being," she said.
The former vice president went on offense, pressing Sanders and Warren on how they would foot the 10-year, $32 trillion bill for their proposal.
Sanders reminded viewers that he "wrote the damn bill" -- which is notable because health care is the rare issue on which Warren does not have her own plan; she backs Sanders' Medicare for All proposal. And he argued it's "the most cost-effective approach to providing health care" to everyone in the country.
Warren ducked a question on whether she would raise middle-class taxes to pay for Medicare for All. And the way she framed her non-answer -- focusing on the overall cost of health care, rather than whether it's paid via income taxes or deductibles and co-pays -- showed how she could make her case in a general election.
"The richest individuals and the biggest corporations are going to pay more, and middle-class families are going to pay less. That's how this is going to work," she said.
3. The centrists fight back
Biden got some back-up on health care Thursday night from his fellow moderates in the race -- most pointedly, Buttigieg and Minnesota Sen.Amy Klobuchar.
"While Bernie wrote the bill, I read the bill," Klobuchar said. "And on page 8 -- on page 8 of the bill, it says that we will no longer have private insurance as we know it. And that means that 149 million Americans will no longer be able to have their current insurance."
"The problem, Sen. Sanders, with that damn bill that you wrote and that Sen. Warren backs is that it doesn't trust the American people," Buttigieg said. Turning to the audience, he said, "I trust you to choose what makes the most sense for you, not my way or the highway."
It was a notable shift in the tenor of a health care debate that had, to this point in the race, largely been dominated by the progressive candidates. In the first debate, liberal agitators like New York City Mayor Bill de Blasio were there to pounce against candidates who were not eager to eliminate private insurance. And in the second debate, Warren and Sanders stood side-by-side and batted away criticism from candidates who didn't qualify for the third debate.
4. Beto breaks out
In front of a home-state crowd, former Texas Rep. Beto O'Rourke finally had the kind of night that showed why he'd once been seen as a phenom.
His biggest moment came when he forcefully argued for the mandatory buyback of assault-style firearms.
"Hell, yes, we're going to take your AR-15, your AK-47. We're not going to allow it to be used against our fellow Americans anymore," he said.
O'Rourke's comment positioned him as a leader in the party's push for gun control (to the chagrin of New Jersey Sen. Cory Booker, who had advanced a similar proposal earlier).
That's right where O'Rourke wants to be, in the wake of the early August mass shooting in his hometown of El Paso that he has said changed him as a candidate. And it was teed up by other Democrats, including Biden, California Sen. Kamala Harris and Castro, who praised him for how he'd returned home to try to help El Paso heal.
Another big moment for O'Rourke came at the end of a riff on racism, when he said of Trump: "We have a white supremacist in the White House and he poses a mortal threat to people of color across this country."
O'Rourke's campaign was ready for a spike in Google searches and social media traffic that followed. His website was overhauled to feature a menacing red image of Trump with the words "The President of the United States of America is a white supremacist" -- as well as lots of links to Trump's racist comments.
5. Harris shifts her focus
In the first debate, it was Harris who had been Biden's chief tormenter -- earning her a surge up the polls that wound up fizzling in July and August.
So she tried a new approach Thursday night, instead taking aim at Trump.
She dedicated her entire opening statement to Trump, addressing him directly as if he was watchin -- which was unlikely, given his speaking engagement in Baltimore -- before closing by saying, "And now, President Trump, you can go back to watching Fox News."
Explaining her shift in strategy to CNN after the debate, Harris said, "My whole campaign is about that and that's why I'm running to unseat him."
"Listen, I believe that there is one common goal that we all have that we need to focus on. And frankly, when we think about this discussion among Democrats, everyone I think should be really clear about pointing out of course, where we disagree, but the ultimate goal has to be to understand that we need a president United States who understands that we need to bring people together," she said.
She tried to be a unifying voice during the health care debate. "Let's talk about the fact that Donald Trump came into office and spent almost the entire first year of his term trying to get rid of the Affordable Care Act," she said.
She also praised the architects of Obamacare, which laid the groundwork for the moderate candidates' plans, and Medicare for All.
"I want to give credit first to Barack Obama for really bringing us this far," she said, then added: "I want to give credit to Bernie. Take credit, Bernie."
6. Buttigieg's 'setback'
Near the end of the debate, ABC moderators asked the candidates an unusual question: What had been their most significant professional setback?
It opened the door for Buttigieg, who is gay, to remind viewers of the historic nature of his candidacy -- and what he has overcome to get into the upper tiers of Democratic presidential candidates.
"As a military officer serving under 'Don't Ask Don't Tell' and as an elected official in the state of Indiana when Mike Pence was governor," he said, "at a certain point, when it came to professional setbacks, I had to wondering whether just acknowledging who I was going to be the ultimate career-ending professional setback."
7. They've got jokes
Democrats tried to be funny.
Sometimes they failed -- like when Klobuchar, referring to Trump, went for the too-obvious "Houston, we have a problem," or when Harris needled Biden over his resistance to executive orders on guns by saying, "Instead of saying 'no we can't,' let's say 'yes we can.'"
Entrepreneur Andrew Yang went with a stereotype. "I am Asian, so I know a lot of doctors," he said.
Others deserved a little bit of a chuckle. The bald Booker, for example, said of the Canadian prime minister Justin Trudeau, "I'm the only person on this stage that finds Trudeau's hair menacing."
Harris, meanwhile, said of Trump that "on trade policy, he reminds me of that guy in 'The Wizard of Oz.' When you pull back the curtain, it's a really small dude."
The vegan Booker, who doesn't have children but is the campaign's most frequent teller of dad jokes, was asked whether Iowans and Texans should follow his example. "First of all I want to say: no. I want to translate that into Spanish: No," he said.
