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.