During the Democratic debate in Detroit, the Massachusetts senator pushed back at moderate criticism by questioning why anyone would run for president just "to talk about what we can't do."
Warren is defending single-payer health insurance and other "big ideas" as policy fights worth having.
She is responding to critics including former Colorado Gov. John Hickenlooper, former Maryland Rep. John Delaney and Montana Gov. Steve Bullock.
Delaney says Warren's and Sen. Bernie Sanders' health care proposals are "dead on arrival" because they would essentially outlaw private health insurance.