Top aides have privately made the case to President Trump in recent days that Iran’s power-generating facilities and bridges are legitimate military targets because destroying them could cripple the country’s missile and nuclear programs, officials say. Trump embraced the rationale, sharply questioned by legal experts and human-rights groups, in a nationwide address Wednesday when he vowed to bomb Iran “back to the stone ages.” By Saturday, as an urgent rescue mission was under way to find a missing U.S. aviator whose aircraft was shot down in Iran, the president showed no signs of backing down on the new strategy. “Remember...