Walmart stepped forcefully into the national gun debate on Tuesday, saying it would stop selling ammunition that can be used in military-style assault rifles, would discourage its customers from openly carrying guns in its stores and would call on Congress to increase background checks and consider a new assault rifle ban... Walmart said it made the announcement after weeks of discussion and research about how best to respond. The decision is in line with public opinion polls that favor more gun controls, and advocates, gun violence victims and others have increasingly called for action. The company said that after “selling through our current inventory commitments,” which could take several weeks, it would stop selling certain short-barrel rifle ammunition and all handgun ammunition... It called on leaders in Washington to enact stronger background checks to “remove weapons from those who have been determined to pose an imminent danger.” The company said it also supported a new debate over an assault rifle ban... “As we’ve seen before, these horrific events occur and then the spotlight fades,” Walmart’s chief executive, Doug McMillon, said in the statement. “We should not allow that to happen. Congress and the administration should act.”