Over the weekend, reports of a secret whistle-blower complaint against President Trump turned into allegations that the president had courted foreign interference from Ukraine to hurt a leading Democratic rival, former Vice President Joseph R. Biden Jr. Mr. Trump called the allegations a “witch hunt” and accused Mr. Biden of corruption. Guest: Michael S. Schmidt, who covers national security and federal investigations for The New York Times. For more information on today’s episode, visit nytimes.com/thedaily.  Background reading: President Trump acknowledged that he discussed Mr. Biden during a phone call with Ukraine’s president, but he did not directly confirm news reports that he had pressured the foreign leader for an investigation.Here’s what we know about the role of Mr. Biden and his son Hunter in the controversy.