Attacks by Houthi militants on shipping in the Red Sea, a crucial global trade route, once seemed like a dangerous sideshow to the war in Gaza. But as the attacks have continued, the sideshow has turned into a full-blown crisis. Vivian Nereim, the Gulf bureau chief for The Times, explains what cause is served by the Houthis’ campaign. Guest: Vivian Nereim, the Gulf bureau chief for The New York Times.