A divided U.S. Supreme Court on Monday allowed states to continue to ban semiautomatic AR-15-style rifles, which can be fired repeatedly without reloading and are owned by millions of Americans. But the issue is far from settled. Only two of the nine justices, Clarence Thomas and Samuel Alito, dissented from the court’s decision to deny review of a federal appeals court ruling in September that upheld Maryland’s AR-15 ban, similar to laws in California and seven other states.