It's one question Democratic presidential candidate Elizabeth Warren won't answer.

Try as they might, and despite repeated attempts, CNN's debate moderators could not extract a straight answer from Warren about whether her healthcare plan — she's a supporter of Medicare for All — would force her to raise taxes.

Her competitors didn't have much better luck.

South Bend mayor Pete Buttigieg accused Warren of dodging the question but couldn't extract an answer.

"A yes or no question that didn't get a yes or no answer," Buttigieg said. "This is why people here in the Midwest are so frustrated with Washington in general and Capitol Hill in particular. Your signature, senator, is to have a plan for everything except this. No plan has been laid out to explain how a multi-trillion-dollar hole in this Medicare for All plan that Senator Warren is putting forward is supposed to get filled in."

Warren replied simply that costs would rise for "the wealthy" and "big corporations" but not for "middle class families."