At a rally in New York City last weekend, Senator Bernie Sanders drew the largest crowd of his presidential campaign — at a moment when his candidacy may be at its most vulnerable. After a heart attack this month, Mr. Sanders faced a challenge in convincing voters that he had the stamina to run both a campaign and the country. His first rally since his hospital stay attracted supporters still resentful of his loss in 2016, and of a party establishment they feel favored Hillary Clinton over Mr. Sanders in the primary. The question for Democratic candidates now is how to respond to this grievance and harness the fervor of Sanders supporters to mobilize support for the Democratic Party more broadly. Guest: Alexander Burns, who covers national politics for The Times. For more information on today’s episode, visit nytimes.com/thedaily.  Background coverage: Revitalized by an endorsement from Representative Alexandria Ocasio-Cortez, Sanders proclaimed “I am back” as he rebooted his cam...