Why is the 37-year-old mayor of South Bend, Ind., running for president — and what would he do if he won? David Leonhardt sits down with Pete Buttigieg to discuss the radicalization of the Republican Party and his plan to resuscitate American democracy. Then, Ross Douthat, Michelle Goldberg and David debate Buttigieg’s unconventional candidacy. For background reading on this episode, visit nytimes.com/theargument