The White House’s recent announcement that President Barack Obama will be the first sitting U.S. president to visit Hiroshima has sparked an intense debate among politicians and pundits over what he should or should not say there. The president’s advisers insist that he “will not revisit the decision” to use nuclear weapons on that city in August 1945.

But the controversy has focused too narrowly on historical questions. We might instead ask whether the U.S., in similar circumstances today, would drop the bomb again. Our...