WASHINGTON — More than a month after North Korea pledged to immediately return some American war dead, the promise is unfulfilled. Secretary of State Mike Pompeo, who traveled to Pyongyang this month to press the North Koreans further, said Wednesday the return could begin “in the next couple of weeks.” But it could take months or years to positively identify the bones as those of specific American servicemen. In a joint statement at their Singapore summit, President Donald Trump and North Korean leader Kim Jong Un committed to recovering the remains of prisoners of war and those missing in action decades after the Korean War — “including the immediate repatriation of those already identified.” That was more than a month ago, on June 12.