President Donald Trump expanded access to a coronavirus treatment that involves blood plasma donated by people who’ve recovered from Covid-19. But while convalescent plasma, as it’s known, is a promising therapy, researchers don’t yet fully understand how well it works. Michelle Fay Cortez explains what the announcement means, and the concerns that agencies like the FDA are letting pressure from the White House, rather than science, guide their decisions.See omnystudio.com/listener for privacy information.