Was Kamala Harris’s debate-stage takedown the beginning of the end for Joe Biden’s frontrunner status? Columnists Ross Douthat, Michelle Goldberg and David Leonhardt take stock of the 2020 Democratic primary so far. Then, are the presidential candidates moving too far to the left? How can the party build a winning coalition? How should they weigh economic versus cultural issues? And which candidates will be able to pivot for a general election audience? For background reading on this episode, visit nytimes.com/theargument.