O'Malley made the comment when speaking about his position on an assault weapons ban and whether as president he would have the automatic weapons confiscated.
"I would not. And that's not what we did in Maryland," he said. "But you know what we did in Maryland? We overcame the NRA's objections. We overcame all of the crowds that were coming down there. We did our own rallies. And at least if we enact these laws in a prospective way we can address a major vulnerability in our country."
"ISIL training videos are telling lone wolfs the easiest way to buy a combat assault weapon in America is at a gun show, and it's because of the flip-flopping political approach of Washington that both of my two colleagues on the stage have represented for the last 40 years," he said.
Vermont Sen. Bernie Sanders cut him off, telling O'Malley: "Whoa, whoa, whoa. Let's calm down a little bit, Martin."
"Yeah, let's tell the truth, Martin," Clinton said.
Throughout the evening, O'Malley, who is polling behind Clinton and Sanders, used strong language to show his exasperation.
"For crying out loud, our country has been attacked," O'Malley said, pivoting the conversation after Sanders apologized to Clinton for his campaign's access of her voter data.
"We have pressing issues involving how we're going to adapt to this changing era of warfare," he said. "Our economy, people are working harder and being left behind. You want to know why things don't get done in Washington? Because for the last 24 hours with those issues being so urgent to people as they tune in tonight, wondering how they're going to even be able to buy presents for their kids, instead we're listening to the bickering back and forth. Maybe that's normal politics in Washington. But that is not the politics of higher purpose that people expect from our party."