The feud between South Bend, Indiana, Mayor Pete Buttigieg and former Rep. Beto O’Rourke boiled over Tuesday during the Democratic debate.

The disagreement between the two, which began in September, centered on conflict over a mandatory assault weapons buyback, a policy that O’Rourke supports. While O’Rourke has argued that a buyback would help curb gun violence, Buttigieg has previously called it a “shiny object” and did not hold back from reiterating this argument again on Tuesday.

“Congressman, you just made it clear you are don’t know how this is actually going to take weapons off the streets,” the mayor said Tuesday, suggesting that O’Rourke was pushing for a “purity test” instead of more pragmatic policy. “If you can develop the plan further, I think we can have a debate about it. But we can’t wait.”

In response, O’Rourke emphasizedthat he does in fact have a plan and that beyond buybacks, he supports other gun reforms, like red flag laws and universal background checks. O’Rourke also worked to make the case that aggressive reforms are the best way to serve the 40,000 annual gun violence victims and countless activists he says he is advocating for.

However, when pressed on how he would implement a mandatory assault weapons buyback on Tuesday, O’Rourke stopped short of explaining how he would confiscate weapons from people who refrain from voluntarily turning them into law enforcement, and don’t bring them to public spaces.

As a campaign spokesperson summed up, enforcement of the policy would go as follows: “Officers would not go door to door, and they would enforce the ban by empowering officers to take those weapons from people when they bring them into the public space.” The spokesperson noted that most people would be expected to comply with the law voluntarily.

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O’Rourke ultimately responded by trying to flip Buttigieg’s attack on its head: “Let’s ... lead and not be limited by the polls and consultants and focus groups,” he said.

The mayor responded forcefully by noting that he didn’t need a lecture from O’Rourke.

“The problem isn’t the polls; the problem is the policy,” he said. “I don’t need lessons from you on courage, political or personal.”

Amid a clash over Beto O'Rourke's proposed mandatory buy-backs of assault-style rifles, Pete Buttigieg tells O'Rourke, "The problem isn’t the polls, the problem is the policy. And I don’t need lessons from you on courage, political or personal." #DemDebate https://t.co/GnrM5echj6 pic.twitter.com/7nNDPqISqp — CNN (@CNN) October 16, 2019

The exchange between the two lawmakers was the most high-profile back-and-forth they’ve had on the subject of gun control, and it was one of several instances in which Buttigieg argued a rival’s policies were too extreme and overly vague. Buttigieg took the same route earlier in the debate when he confronted Sen. Elizabeth Warren on the subject of Medicare-for-all and argued that she was pushing a more progressive idea instead of focusing on other proposals that could also help expand health care coverage.

On both subjects, O’Rourke and Warren responded to the mayor by saying that their focus on ambitious policies was intended to be a stronger and more effective response to the respective issues of health care coverage and gun control. Warren argued that Buttigieg’s health care proposal, something he’s been referring to as Medicare-for-all-who-want-it, was actually only accessible to those who could afford it. O’Rourke, too, noted that more aggressive measures like a buyback would be necessary to address gun violence.

The spirited discussion on the two topics marked moments where Buttigieg sought to differentiate himself as a moderate option and frame himself as a foil to other candidates onstage. Polling steadily in the middle of the pack, according to the RealClearPolitics polling average, Buttigieg needed a strong performance in Tuesday’s debate to further carve out a niche for himself.

Taking on O’Rourke — and Warren — was apparently part of that strategy.