People in the Syrian town of Madaya are still starving to death. A U.N. aid convoy was finally allowed into the town last month, but it wasn't enough. Secretary of State John Kerry says that's because the Syrian government has surrounded the town and is not allowing enough aid in. Anti-government rebels have also besieged towns in Syria, which Kerry called "directly contrary to the law of war." Is starvation a war crime? NPR's Kelly McEvers talks to law professor Beth Van Schaack to explain.