Dr. Anthony Fauci is the nation's top expert on infectious diseases. It's clear in media reports that he and President Trump don't readily agree on the severity of the pandemic. As that plays out on the national stage, Dr. Fauci recently spoke at the Aspen Ideas Festival in Colorado. It was held virtually this year due to the pandemic. CNN's senior medical correspondent Elizabeth Cohen asked him questions. Today we share an excerpt of that discussion, focusing on the effort to come up with a vaccine to prevent COVID-19, the challenges of contact tracing, and why the virus is especially frustrating for doctors. Audio is courtesy of the Aspen Institute.