December has been the deadliest month in the U.S. since the coronavirus pandemic began. Dr. Anthony Fauci has warned about a post-holiday surge in coronavirus infections, saying the darkest days may be ahead of us. Dr. Celine Gounder, clinical assistant professor of medicine and infectious diseases at NYU's Grossman School of Medicine and member of Biden's Covid-19 task force, joins "Squawk Box" to discuss.