Tuesday marks the last time the leading Democratic presidential contenders will face a national audience on the debate stage before primary voting begins, making it the most significant moment of the 2020 primary season to date. The prime-time faceoff comes just 20 days before Iowa’s caucuses as polls suggest the nomination is truly up for grabs. Heading in, there are new signs of tension among all the top-tier candidates, particularly Bernie Sanders and Elizabeth Warren. If ever there has been a time for the six contenders on stage to take the gloves off, this is it.