WASHINGTON (AP) — Elizabeth Warren is rising to the top of the Democratic pack with ambitious promises to reshape the political and economic system. But as she faces growing scrutiny, the Massachusetts senator is opening herself to criticism that she’s just another politician dodging the tough questions.

She is in a bind because of her persistent refusal during two straight presidential debates to say whether she would raise taxes on the middle class to pay for the universal health insurance plan known as “Medicare for All.”

By not acknowledging taxes would almost certainly increase for a wide range of income earners, Warren avoids becoming a caricature of a Democrat itching to raise them. But she also threatens to undermine the image she’s fostered of a plainspoken former professor ready to tackle any issue in her quest to protect the middle class from the excesses of corporations and the wealthy.

Warren’s progressive rival, Bernie Sanders, has said middle-class taxes would have to rise to pay for Medicare for All. Other White House hopefuls said Wednesday that Warren should be just as direct.

“Look, I’m not picking on Elizabeth Warren, but this is ridiculous,” said former Vice President Joe Biden, currently Warren’s chief competitor for the Democratic nomination. Warren “is going to have to tell the truth” or face questions about her willingness “to be candid and honest with the American people.”

Minnesota Sen. Amy Klobuchar said Warren “needs to come forward and say” how she’d pay for a new health insurance system.

“I’m sure she will eventually,” Klobuchar said.

Pete Buttigieg, the mayor of South Bend, Indiana, echoed that thought from the campaign trail in Ames, Iowa.

“Everybody should be prepared to defend their plans,” he said Wednesday. “It’s serving us well to be very clear about how our plan works and to lay out the fact that it’s paid for.”

Warren argues pundits are missing the point by focusing on taxes instead of the bottom-line cost that Americans pay for their health care.