Three years after the start of Covid, the central mystery of the pandemic — how exactly it began — remains unsolved. But recently, the debate about the source of the coronavirus has re-emerged, this time in Congress.The Energy Department has concluded, with “low confidence,” that an accidental laboratory leak in China was most likely the origin, but politics are making it harder to find definitive answers.Guest: Benjamin Mueller, a health and science correspondent for The New York Times.Background reading: Republicans have pushed the lab leak theory, but they lack a “smoking gun.”What we know and don’t know about the origins of Covid.For more information on today’s episode, visit nytimes.com/thedaily. Transcripts of each episode will be made available by the next workday.