With crowds that are said to number 15,000 to 20,000 people, Senator Elizabeth Warren’s campaign events frequently dwarf those of her Democratic rivals. This week, we experienced the growing phenomenon that is the Warren rally. Guest: Thomas Kaplan, a political reporter for The New York Times. For more information on today’s episode, visit nytimes.com/thedaily.  Background reading: Ms. Warren, running on a message of sweeping change, is solidifying her place in an exclusive club of presidential candidates who have become crowd magnets.At her campaign events, Ms. Warren’s speech is only the first act. Act Two? The selfie line.Back-to-back rallies by Ms. Warren and President Trump laid out competing versions of populism that could come to define the 2020 presidential campaign.