President Obama has had some trying experiences since he took office in January 2009, but this month’s shooting at Sandy Hook Elementary School in Newtown, Conn., was the toughest. On NBC’s Meet the Press Sunday morning, the president reflected on the tragic incident, saying, “That was the worst day of my presidency, and it’s not something I want to see repeated.” Obama also incited public demand for gun-control laws and expressed concern over the push to arm school staff.