Sen. Elizabeth Warren, D-Mass, called Donald Trump “a loser” Monday in a series of increasingly critical tweets about the billionaire businessman.

“Let’s be honest — [Trump] is a loser. Count all his failed businesses. See how he cheated people [with] scams like Trump U,” she said in the first of many notes. “See how [Trump] kept his father’s empire afloat using strategic corporate bankruptcies to skip out on debt.”