About an hour into Thursday night’s Democratic debate, David Muir, one of the moderators, turned to the recent string of deadly mass shootings in the country. Two of the massacres had taken place in Texas, where the debate was being held. On August 3rd, a gunman killed twenty-two people at a Walmart in El Paso. Less than a month later, another shooter killed seven people in an attack that took place between Odessa and Midland.

Muir asked Beto O’Rourke, the former congressman from El Paso, about his decision last month, in the wake of the tragedy in his community, to call for a mandatory buyback of assault weapons. O’Rourke’s proposal positioned him as, by far, the most aggressive of the remaining Democratic contenders on guns. (Representative Eric Swalwell, of California, who ended his Presidential campaign in July, had also called for a mandatory buyback of assault weapons.)

Muir invoked the language that gun-rights advocates have often used to instill fear among gun owners about firearm restrictions: “You know, the critics call this confiscation,” Muir said. “Are you proposing taking away their guns, and how would this work?”

Unlike legions of past Democratic candidates, O’Rourke didn’t flinch. “I am,” he said. “If it’s a weapon that was designed to kill people on a battlefield—if the high-impact, high-velocity round, when it hits your body, shreds everything inside of your body, because it was designed to do that.”

O’Rourke’s early promise as a candidate sprang from his talents as a brooding, sermonizing communicator. Behind the lectern, he started to gather himself and quicken his pace, gesturing with his hands to punctuate his points and summon the gravity he wanted to convey. “And in Odessa, I met the mother of a fifteen-year-old girl who was shot by an AR-15, and that mother watched her bleed to death, over the course of an hour,” he said, “because so many other people were shot by that AR-15 in Odessa, in Midland, there weren’t enough ambulances to get to them in time.” He was shouting now.

“Hell, yes, we’re going to take your AR-15, your AK-47,” O’Rourke said, finishing to cheers and applause from the audience.

It was a stirring moment, in a campaign that has been short on them. It may prove too late to resuscitate O’Rourke’s struggling campaign. (Before the debate was over, his campaign was selling T-shirts online for thirty dollars emblazoned with his memorable line.) Yet its significance could outlast O’Rourke. In recent weeks, a few of his rival candidates have begun to signal openness to the idea of mandatory buybacks as well. Finally, the Democratic conversation on guns is getting bolder.