DES MOINES, Iowa – Elizabeth Warren made a forceful case for a female president and stood behind her accusation suggesting sexism by progressive rival Bernie Sanders Tuesday night in a Democratic debate that raised gender as a key issue in the sprint to Iowa’s presidential caucuses. Sanders vehemently denied Warren's accusation, which threatened to split the Democratic Party’s left flank -- as well as the senators' longtime liberal alliance -- at a critical moment less than three weeks before voting begins. “Look at the men on this stage.