The U.S. Supreme Court on Monday debated the insanity defense in criminal prosecutions and delivered a potential setback to gun control advocates as it opened its new term on Monday with a flurry of activity on a day when its longest-serving justice, Clarence Thomas, was absent due to illness. The conservative-majority court returned after a three-month break to launch its new nine-month term with arguments in a trio of cases. The court hears the term’s first major case on Tuesday on whether a landmark federal anti-discrimination law that bars sex discrimination in the workplace protects gay and transgender employees.