Twenty Democratic presidential candidates have appeared on the debate stage for the last time. That’s in part because the Democratic National Committee has introduced a set of rules explicitly designed to narrow the field. We look at the intended and unintended consequences of that change. Guest: Reid J. Epstein, a political reporter for The New York Times. For more information on today’s episode, visit nytimes.com/thedaily.  Background reading: It will be twice as hard for the 2020 Democrats to qualify for the next debate. In addition to the seven who already have, three are within striking distance.Democratic candidates aiming to replace President Trump are forced to choose between adopting his media tactics or being left behind as others do.