Tree of Life synagogue had practiced active-shooter drills. Staff members knew the protocols, and they had assessed the building’s security just last year. On high holidays, police officers would keep watch outside the synagogue. But like many synagogues across the country, Tree of Life had its doors open for Saturday’s Shabbat services, welcoming its congregants. After a gunman entered and killed 11 people in the worst single attack on American Jews in U.S. history, President Trump and others have suggested that armed guards stationed outside the synagogue might have prevented the carnage. Read more.