Tensions between the two Midwesterners on the stage, Amy Klobuchar and Pete Buttigieg, boiled over on the debate stage in Las Vegas, Nevada, with each accusing the other of lacking the knowledge and experience needed to lead the country.
Buttigieg took aim at Klobuchar for recently forgetting the name of Mexico's president and his policies during a televised interview earlier this week, suggesting she lacks the knowledge to serve as president despite serving on the "committee that's overseeing these things."
Klobuchar, he said, was not "able to speak to literally the first thing about the politics of the country to our south."
"Are you trying to say that I'm dumb?" Klobuchar responded. "Or are you mocking me here, Pete? I said I made an error. People sometimes forget names."
The sparring prompted Elizabeth Warren to jump in to defend Klobuchar and said the attacks are "not right."
But the two continued to go at it as the debate neared its closing minutes after Klobuchar was asked a question about the future of Dreamers, the name given to young immigrants brought to the United States illegally as children.
Buttigieg criticized Klobuchar on her record on immigration, for voting to confirm a Trump-nominated head of Customs and Border Protection and her votes to confirm Trump judicial nominees. As he began to speak in Spanish, Klobuchar mocked, "I wish everyone was as perfect as you, Pete."
The Minnesota senator said she has been "in the arena," unlike the former South Bend mayor, and she countered that the unnamed CBP nominee, Kevin McAleenan, had been recommended by Obama administration officials.
"You've memorized a bunch of talking points and a bunch of things," Klobuchar said.
In response, Buttigieg accused Klobuchar of suggesting his experience as a mayor didn't measure up.
"I'm used to senators telling mayors that senators are more important than mayors," he said. "You don't have to be in Washington to matter."
Klobuchar, who has seen her candidacy surge in recent weeks, and Buttigieg, who placed first in Iowa and second in New Hampshire, are both striving to be the choice of moderate Democrats in the battle for the nomination.
Six candidates in all were on the debate stage Wednesday, including Michael Bloomberg, who made his first appearance.