Without question the sharpest and most unforgettable exchange of the night was when Castro sought a breakout moment by using a minor point in the health care debate to suggest that Biden was losing his memory.
Coming off a spirited ideological debate with Sanders and Warren about his view that their “Medicare for All” proposal is too expensive and will burden American taxpayers, Biden off-handedly made a point about his own plan: “Anyone who can’t afford it gets automatically enrolled in the Medicare-type option we have.”
Castro aggressively cut Biden off with a jab about his age.
“Are you forgetting what you said two minutes ago? Are you forgetting already what you said just two minutes ago?” Castro said, as the other candidates looked on, slightly aghast. “I mean, I can’t believe that you said two minutes ago that they had to buy in and now you’re saying they don’t have to buy in. You’re forgetting that.”
Castro went on to say — in a point that was only partly correct — that his health care plan unlike Biden’s, would automatically enroll Americans who lost their jobs. “I’m fulfilling the legacy of Barack Obama and you are not,” Castro said in a final joust to Biden.
“That will be a surprise to him,” Biden replied.
It was a stunning moment in a race where the younger contenders have often argued — more gently perhaps — that it is time for a new generation of leadership. In making that argument, Castro was attempting to relfect the concern voiced by many Democratic voters that Biden does not seem as sharp as he did during his eight years as Obama’s vice president.
But the former San Antonio’s mayor attack was so cringe-worthy that several other candidates felt the need to step in.
“This reminds everybody of what they cannot stand about Washington, scoring points against each other, poking at each other,” Buttigieg said.
“Yeah, that’s called the Democratic primary election, Pete,” Castro snapped back. “That’s called an election.”
“Yes, but a house divided cannot stand,” Minnesota Sen. Amy Klobuchar interjected, drawing applause from the audience. “That is not how we’re going to win this.”
New Jersey Sen. Cory Booker closed out the exchange with a plea for unity and an attempt to steer the debate back to a more substantive discussion.
“Look, there are a lot of people watching at home right now, listening to us, that are afraid because they are in crisis,” Booker said.
He added, “This must be a moment where we, as Democrats, can begin to show that we cannot only stake and stand our ground, but find common ground. Because we’ve got one shot to make Donald Trump a one-term president.”
Candidates swing, and a few miss
While the spat between Castro and Biden was the most memorable exchange of the night, other candidates also managed to leave some shaking their heads.
California Sen. Kamala Harris had a more uneven night than in prior debates. Several of her lines that had clearly been rehearsed didn’t land — though at one point when talking about Trump’s trade policy, she said to laughter that the President “reminds me of that guy in ‘The Wizard of Oz,’ you know, when you pull back the curtain, it’s a really small dude?”
Meanwhile, Biden had some strong moments, defending his health care plan early in the debate with Warren and Sanders, for example. But his answers were sometimes unclear, lacking a linear through line as he jumped from point to point.
That was true when he went on a long tangent about his efforts to bring home troops from Afghanistan, and in another exchange when he veered from a question about his position on reparations into an argument that children should listen to the radio or a record player.
His sometimes shaky performance may underscore concerns many Democratic voters have about his ability to take on Trump. But he solidified his performance at the end of the night with a strong answer about how he’s recovered from setbacks.
He noted that he was raised to believe that family is at the center of everything.
“Right after I got elected, my wife and daughter were killed in an automobile accident, and my two sons were badly injured. And I just had been elected, not sworn in. And I lost my faith for a while. I came back,” Biden said. “And then later, when my son Beau came home from Iraq and — with a terminal disease, and a year later, year-and-a-half later, losing him was like losing part of my soul. But the fact is that I learned that the way you deal with it — is you deal with it by finding purpose, purpose in what you do. And that’s why I hope — I hope he’s proud of me today.”
After a long pause, Buttigieg — who happened to be up next in the line of opening statements — dryly quipped: “It’s original, I’ll give you that.”
Gun control gains new prominence after shootings
Booker skillfully turned specific policy questions into eloquent arguments about the need to unify America. When the debate turned to the series of mass shootings, for example, Booker argued that America needed to show more “courageous empathy.”
“We are never going to solve this crisis if we have to wait for it to personally affect us or our neighborhood or our community before we demand action,” Booker said, noting his own experience with gun violence as mayor of Newark.
“I have seen what the carnage creates in communities like mine, because we forget — national shootings, these mass shootings are tragedies, but the majority of the homicide victims come from neighborhoods like mine,” Booker said.
The night was a strong one not only for Booker, who has repeatedly showed his command of the finer points of debating, but also for O’Rourke, who has often seemed out of his depth when sharing the stage with his more experienced rivals.
After the massacre in his hometown of El Paso, O’Rourke suspended his campaign for nearly two weeks to meet with victims’ families and tend to his community.
He spoke with passion about that experience Thursday night and did not shy away from a moderator’s question about whether he would confiscate assault-style weapons.
“Are you proposing taking away their guns?” ABC moderator David Muir asked.
“I am, if it’s a weapon that was designed to kill people on a battlefield,” O’Rourke said, adding, “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.”
Health care once again exposes divide
Biden, whose camp had made clear before the debate that he planned to go after Warren, quickly made good on that promise by attempting to distance her from Obama, who remains one of the most popular figures in the Democratic Party.
“I know that the senator says she’s for Bernie, I’m for Barack,” Biden said. “I think the Obamacare worked. I think the way we add to it, replace everything that’s been cut, add a public option, guarantee that everyone will be able to have affordable insurance number one.”
Sidestepping the opportunity to attack Biden, Warren chose to be gracious — complimenting the work of the Obama administration on health care. She would not — at the moderator’s prompting — say that middle class Americans’ taxes would go up, but she defended her plan.
“I actually never met anybody who likes their health insurance company. I’ve met people who like their doctors,” she said, along with their nurses, their pharmacists and their physical therapists. She added that Americans don’t want to spend all their time fighting with insurance companies.
Sanders, who has been praised by Biden as being honest with the American people that their taxes would go up if the country moves to “Medicare for All,” weighed in by citing the costs the country would bear if the nation does not move to Medicare for All.
“Americans don’t want to pay twice as much as other countries, and they guarantee health care for all people,” Sanders said.
This story has been updated.
CNN’s Jeff Zeleny contributed to this report.