Meghan McCain responded after Harris paid homage to her late father, Sen. John McCain, while she spoke about the Affordable Care Act.

Things got a little confusing in the debate when former Housing Secretary Julián Castro accused former Vice President Joe Biden of forgetting what he had said earlier on health care — an exchange that drew attention for perhaps implying an attack on Biden’s age and memory.

The clash came after Castro criticized Biden’s health care plan for not automatically enrolling all uninsured Americans in a Medicare-like plan, as Castro says his plan would do.

“The difference between what I support and what you support, Vice President Biden, is that you require them to opt in and I would not require them to opt in, they would automatically be enrolled — they wouldn't have to buy in,” Castro said. “That's a big difference, because Barack Obama's vision was not to leave 10 million people uncovered.”

When Biden protested that “they would not have to buy in,” Castro said he was contradicting an earlier claim that people would have to “buy in” to Medicare. Biden responded, “I said if they can’t afford it!”

Two issues are at play here: One is the narrow issue of what Biden said earlier; two is a disagreement between the two on health care policy. Read more about what was really going on in the dust-up.

A Texas state representative had a menacing response to Beto O'Rourke's statement in Thursday's debate that "hell yes, we're going to take your AR-15."

"My AR is ready for you Robert Francis," Republican Representative Briscoe Cain tweeted about O'Rourke, using the presidential candidate's legal first and middle name.

Cain's tweet was heavily ratioed on Twitter, meaning it received more outraged comments than likes or retweets. Within three hours, 3,400 people had commented on the post, and 89 people retweeted it.

O'Rourke was one of those who was upset. "This is a death threat, Representative. Clearly, you shouldn't own an AR-15 — and neither should anyone else," he wrote.

When asked about mandatory buybacks for assault weapons during the debate, O'Rourke's response drew loud applause: "Hell yes, we're going to take your AR-15, your AK-47," he said. "We're not going to allow it to be used against our fellow Americans anymore. If it's a weapon that was designed to kill people on the battlefield, we're going to buy it back."

At one point, Sanders claimed, "We have the highest child poverty rate of almost any country on Earth."

This is hyperbole — there are numerous less-developed nations with higher child poverty rates.

America's child poverty rate is above the Organisation for Economic Co-operation and Development average, but a slew of other countries have even higher child poverty rates, including Russia, Spain, India, Israel, Brazil and China.

Buttigieg told a story about a Japanese exchange student in Indiana who returned to her home country and, after failing to pass a teacher’s exam, became a doctor — seeming to imply that teachers in Japan are compensated on par with those in the medical profession. 

“She took the exam to try to become a teacher in a society that really regards teachers and compensates teachers well. And she came up just short. So, you know what she did? Since she was academically good but couldn't quite make the cut to be a teacher, she had a fall-back plan; she became a doctor. That is how seriously some countries treat the teaching profession. If we want to get the results that we expect for our children, we have to support and compensate the teaching profession. Respect teachers the way we do soldiers and pay them more like the way we do doctors,” Buttigieg said.

According to data from the intergovernmental Organisation for Economic Co-operation and Development (OECD), American teachers are actually paid better than Japanese teachers.

Primary school teachers in Japan with 15 years' experience make approximately $51,000 a year. American primary school teachers with the same level of experience make approximately $62,000 a year.

Luxembourg might have been a better example: Teachers at this level make $104,000 a year.

Elizabeth Warren, in defending her campaign position that she would roll back the legislative filibuster — a move that would allow Senate bills to advance to a full vote with a simple majority instead of the 60 the modern filibuster requires to end debate on a bill and move on to the vote — made the claim that “we’re not going to get anything done on guns” without her proposed roll-back.

“I was in the United States Senate when 54 senators said let's do background checks, let's get rid of assault weapons, and with 54 senators, it failed because of the filibuster,” she said.

This isn’t exactly true. Warren appears to be conflating two separate votes.

In 2013, following the December 2012 Newtown, Connecticut, massacre at Sandy Hook Elementary School, the Senate held several votes on gun control bills. At the time, Democrats (as well as Independents that aligned with Democrats) controlled 55 seats in the Senate.

One vote was for a bill to expand and strengthen background checks on gun sales. Another vote was for a bill to ban assault weapons. Both failed. The so-called “Manchin-Toomey” compromise on background checks failed 54-46, meaning it could have passed a filibuster-free Senate, as Warren claimed Thursday.

But only 40 senators voted for the assault weapons ban (it failed 60-40), meaning a filibuster-free Senate could have not saved it. 

Biden campaign advisers Kate Bedingfield, Anita Dunn and Symone Sanders scrummed in the spin room. Asked about the healthcare exchange with Castro, Dunn referred to it as a cheap shot and said he hasn’t learned the lesson other candidates at previous debates learned: that these attacks on Biden backfire.

"It was a cheap shot and a question Castro should answer," Dunn said.

Castro addresses his attacks on Biden in a post-debate interview with ABC.

"I wasn't taking a shot at his age," Castro said. "It's about the health care policy."

Republican National Committee Chairwoman Ronna McDaniel said in a post-debate statement that the Democratic contenders would hurt U.S. communities with what she described as their “radical, socialist policies.” 

“Tonight’s debate featured no new ideas to empower Americans as they work and raise their families. Instead, Democrats again promised tax hikes, ending private health insurance, and a total government takeover of our lives,” said McDaniel, adding, “President Trump will continue to fight for the American people.”

Trump’s re-election campaign echoed that message, with spokesperson Kayleigh McEnany saying that Democrats’ “big government socialism would force a government takeover of healthcare, eliminate private insurance, provide free healthcare to illegal immigrants, kill millions of jobs by ending the fossil fuel industry, disarm the American public, and raise taxes to pay for their radical agenda.”

"Over 90 percent of the American people think we have to get assault weapons off the street — period. And we have to get buy-backs and get them out of their basements," Biden said during Thursday night's debate.

This is an exaggeration. Americans tend to support banning the sale of assault rifles, but mandatory buybacks are another question. 

According to a Politico/Morning Consult poll conducted last month, 70 percent of Americans said they support banning assault-style weapons. A Monmouth University survey this month found that 56 percent of Americans approve of a ban on assault rifles, but support falls dramatically when it comes to giving up the guns they already own. Just 43 percent of respondents supported a mandatory buyback program in the Monmouth survey. 

And when Gallup asked in 2018 if respondents would be “for or against” a law making it illegal to manufacture, sell or possess semi-automatic guns known as assault rifles, just 40 percent of respondents said they favored such a law.

It was what everyone was looking forward to: Biden, the front-runner since he joined the Democratic race, vs. Warren, who’s been slowly and steadily gaining ground on him. Thursday was the first time the two would be on stage together. 

In the lead-up to the debate, both candidates signaled they’d be drawing contrasts with each other, with Biden’s campaign going the furthest in saying that getting things done was more important than having a lot of "plans." Plus, attention was given to the candidates’ contentious history in the run-up to Thursday.

But the anticipated clash never happened. In fact, the two had little chance to address each other. Biden, Sanders and Warren had an exchange early on regarding one another's health care plans, but that was the extent of it. For a long stretch in the middle of the debate, Warren went without being addressed by the moderators. Biden, meanwhile, was fending off attacks from Castro and others on stage.

As a result, the debate appeared unlikely to move the needle between Biden and Warren.