LAS VEGAS — The simmering Midwestern feud between Senator Amy Klobuchar of Minnesota and Pete Buttigieg erupted on Wednesday night, as the two rivals increasingly turned their cannons on each other in a manner that was by turns caustic and personal.
The fracas ignited in response to a question at the Democratic presidential debate about Ms. Klobuchar’s failure to recall the name of the president of Mexico.
The question, from the moderator Vanessa Hauc of Telemundo, resurfaced an embarrassing gaffe for Ms. Klobuchar that occurred during an interview last week with Telemundo. Ms. Hauc asked about Ms. Klobuchar’s preparedness for foreign policy and economic relations with one of the United States’ closest trading partners.
Ms. Klobuchar, who dismissed the error as “momentary forgetfulness,” instead took umbrage with the attacks that Mr. Buttigieg had lobbed at her over the lapse, at one point accusing Mr. Buttigieg of calling her “dumb” and being overtly personal. And Senator Elizabeth Warren jumped in to defend Ms. Klobuchar, saying her mistake was trivial and had drawn undue attention.
“That’s right, I said I made an error,” Ms. Klobuchar said. “I think having a president that maybe is humble and is able to admit that here and there maybe wouldn’t be a bad thing.”
“I wouldn’t liken this to trivia,” Mr. Buttigieg replied. He added: “You’re staking your candidacy on your Washington experience. You’re on the committee that oversees border security. You’re on the committee that does trade. You’re literally in the part of the committee that’s overseeing these things.”
With a flash of anger, Ms. Klobuchar cut in.
“Are you trying to say that I’m dumb — are you mocking me here, Pete?” Ms. Klobuchar said. “I said I made an error. People sometimes forget names. I am the one that has, No. 1, has the experience based on passing over 100 bills.” She then criticized Mr. Buttigieg’s previous failed runs for office.
The argument between the two candidates grew so heated that Ms. Warren went to Ms. Klobuchar’s defense.
“Can I just defend Senator Klobuchar for a minute?” she said. “This is not right. I understand that she forgot a name. It happens, it happens to everybody on this stage. Look, you want to ask about whether or not you understand trade policy with Mexico? Have at it.”
That seemed to bring a momentary peace between Ms. Klobuchar and Mr. Buttigieg, two candidates who are vying to appeal to the party’s more moderate and centrist voters and emerge as an alternative to Senator Bernie Sanders.
But as the debate stretched deep into its second hour, the two candidates again took aim at each other, this time over experience.
“If you’re going to run based on your record of voting in Washington, then you have to own those votes, especially when it comes to immigration,” Mr. Buttigieg said, turning again to directly face Ms. Klobuchar, pointing to her votes to confirm judges nominated by President Trump, as well as his pick to head U.S. Customs and Border Protection.
“I wish everyone was as perfect as you, Pete, but let me tell you what it’s like to be in the arena,” Ms. Klobuchar said in response, using her favorite euphemism for experience in Washington. She later continued: “You have not been in the arena doing that work. You’ve memorized a bunch of talking points and a bunch of things.”
Mr. Buttigieg, showing a rare hint of frustration, quickly retorted.
“You know, maybe leading a diverse city that was facing ruin doesn’t sound like the arena to you,” he said. “I’m used to senators telling mayors that senators are more important than mayors, but this is the arena, too. You don’t have to be in Washington to matter. You don’t have to be on Capitol Hill for your work to be significant.”
This time, it wasn’t Ms. Warren or another candidate who interjected to separate the two candidates, but Chuck Todd, one of the debate moderators.
“Guys, guys, we are at the end here,” he said. “We are at the end here. I’ve got to let that one go.”