Former Texas congressman Beto O’Rourke and South Bend Mayor Pete Buttigieg sparred over gun safety policies during the fourth Democratic presidential debate in Westerville, Ohio on Tuesday.

The contentious back-and-forth between the two young Democratic White House hopefuls started when CNN anchor Anderson Cooper asked O’Rourke about his campaign pledge to institute a mandatory buyback program for owners of high-powered rifles, such as widely-used variations of the AR-15 and AK-47.

Many critics of the proposal, including Buttigieg, have raised doubts about the feasibility of such a program. Cooper asked O’Rourke how he would enforce the proposal and compel unwilling gun owners to participate.

“I expect my fellow Americans to follow the law,” the Texas Democrat responded. “The same way that we enforce any provision, any law that we have right now. We don’t go door-to-door to do anything in this country to enforce the law.”

Unsatisfied with the answer, Cooper continued to press O’Rourke, asking him how he would ensure that all owners of guns subject to his mandatory buyback initiative agreed to turn in their weapons. The CNN anchor floated the scenario of a gun owner refusing to participate in the proposal.

“If someone does not turn in an AR-15, an AK-47 — one of these weapons of war — or brings it out in public and brandishes in an attempt to intimidate, as we saw when we were at Kent state recently, then that weapon will be taken from them,” O’Rourke said. “If they persist, there will be other consequences from law enforcement. But the expectation is that Americans will follow the law.”

Cooper then turned to Buttigieg, noting that the Midwestern mayor previously called O’Rourke’s plan a form of “confiscation.”

Buttigieg faulted O’Rourke for failing to explain how his proposal would get weapons “off the streets.” He said Democrats need to instead focus on quickly and effectively pushing less controversial gun safety measures, like universal background checks for gun transactions and so-called “red flag” laws.

“We cannot wait for purity tests,” the mayor said. “We have to just get something done.”

The last comment visibly irked O’Rourke, who pushed back on the idea that his buyback program was part of a “purity test.” He said Democrats should not limit their gun safety proposals based on polls or suggestions by political consultants — a not so thinly-veiled jab at Buttigieg.

“I don’t need lessons from you on courage — political or personal,” Buttigieg, who was deployed to Afghanistan during his time in the Navy Reserve, told O’Rourke during a heated part of the exchange.

He advised O’Rourke to focus his criticism on gun lobby groups like the National Rifle Association (NRA), and not fellow Democrats.

O’Rourke, in turn, told Buttigieg that he was not taking anyone on for simply challenging his proposal on policy grounds. But he said that calling his buyback plan a “shiny object” represented a “slap in the face” to survivors of gun violence.

The conversation finally cooled off when Buttigieg pivoted to health care.

Immediately after the exchange between O’Rourke and Buttigieg, Senator Cory Booker of New Jersey, in a more conciliatory tone, urged the rest of the candidates to dial down the rhetoric.

“I worry about how we talk to each other and about each other,” he told the audience.

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