Senator Amy Klobuchar then went in on Sanders’s token line from a previous debate: that he “wrote the damn bill” on Medicare for All. “While Bernie wrote the bill, I read the bill, and on page 8, it says that we will no longer have private insurance as we know it,” Klobuchar said with a sly grin. Buttigieg then jumped into the fray, saying, “The damn bill that [Sanders] wrote, and that Senator Warren backs … doesn’t trust the American people.”

The digs became more personal from there. Biden attacked Sanders directly for his leftist politics, saying, “Let me tell you something: For a Socialist, you have a lot more confidence in corporate America than I do.”

It all crescendoed with Julian Castro saying Biden’s plan would require a buy-in, while his own would not. “They do not have to buy in! They do not have to buy in!” Biden shouted in response.

“You just said that two minutes ago!” Castro said, adding what might have been a jab at Biden’s age: “Are you forgetting what you said two minutes ago?”

It makes sense that the candidates would let their major schisms play out in the health-care space. It’s one of the few domains in which their views reflect a total difference in kind, rather than in degree. The next question was about racism, which nearly everyone agrees is bad. But the Democrats fundamentally disagree on what to do about health care in America. Biden and a few others want to improve on Obamacare, while Warren and Sanders want to completely overhaul the system and replace it with U.K.-style single-payer. The vision that prevails will affect Americans’ lives in sweeping ways.

Plus, perhaps they’ve learned from the winner of the 2016 election that the nice guy doesn’t always finish first in politics. The Democrats are willing to try to get through to voters—even if it’s by using brashness and sarcasm.

After the tense exchange between Castro and Biden, Buttigieg raced in to be the civility police: “This is why presidential debates are becoming unwatchable,” he said. “This reminds everybody of what they cannot stand about Washington.”

“That’s called the Democratic-primary election, Pete,” Castro retorted.

That it is, and if tonight is a guide, it’s heating way up.