Michelle and I were saddened to learn of the passing of Helen Thomas. Helen was a true pioneer, opening doors and breaking down barriers for generations of women in journalism. She covered every White House since President Kennedy's, and during that time she never failed to keep presidents -- myself included -- on their toes. What made Helen the "Dean of the White House Press Corps" was not just the length of her tenure, but her fierce belief that our democracy works best when we ask tough questions and hold our leaders to account. Our thoughts are with Helen's family, her friends, and the colleagues who respected her so deeply.