U.S. Democratic candidates had one last shot in the debate arena Tuesday (January 14) night, before voting starts in Iowa to decide the 2020 nominee in less than three weeks' time. Tom Steyer, Elizabeth Warren, Joe Biden, Bernie Sanders, Pete Buttigieg and Amy Klobuchar took to the stage in the smallest and least-diverse debate to date. Biden - who still leads in polls nationally - needed only a steady performance on the night, and largely delivered it. His main challenge came from Sanders, who sparred with him over foreign policy. A hotbutton issue, as the U.S. and Iran square off raising fears of another conflict in the Middle East. Sanders voted against authorizing war in Iraq more than a decade ago - and he questioned Biden's judgement and ability to lead for instead voting yes. Biden has long touted his resume on national security. He admitted on stage that he made a quote - big, big mistake - in initially voting for the war in Iraq. But he went on to defend his subsequent steps - in his words- to bring the troops home as Vice President. The pair shared a joke about North Korea calling Biden a 'rabid dog' but went back to clashing over the new trade deal with Mexico and Canada. Other candidates also had their say. Especially when the debate turned to the prospect of a woman in the White House. The issue of female electability has become a flashpoint in the Democratic race. According to a CNN report Sanders told Warren in 2018 that he did not believe a woman could win. During the debate he repeated his denial that he ever said that - saying it would be incomprehensible. The tension between the two was palpable. Warren made a high-stakes bet on gender, and made the case that women made for better candidates than men. Tuesday was the last debate before Iowa voters kick off the primary season on February 3rd - to find a November election challenger to President Trump. Three more debates are scheduled later in February.