On New Year’s Day in New Orleans, a man drove a pickup truck into a crowd of people, killing 14 and leaving many others injured. In the aftermath law enforcement found an Islamic State flag in the truck, and evidence that shows the man was inspired by the extremist group. This wasn’t the only Islamic State-inspired incident in recent months.Today on “Post Reports,” guest host Rachel Siegel speaks with national security reporter Joby Warrick about how people become radicalized by the Islamic State and what the New Orleans attack and the canceled Taylor Swift concerts in Austria tell us about the power of extremist propaganda. Warrick’s book “Black Flags: The Rise of ISIS” was awarded a 2016 Pulitzer Prize for nonfiction. Today’s show was produced by Elana Gordon, with help from Ariel Plotnick and Rennie Svirnovskiy. It was edited by Monica Campbell, with help from Reena Flores, and mixed by Sam Bair.Subscribe to The Washington Post here.