President Obama personally apologized on Wednesday to the head of Doctors Without Borders for what he described as the mistaken bombing of its field hospital in Kunduz, Afghanistan, promising a full investigation into the episode, which took the lives of nearly two dozen doctors and patients.br br But five days after an American AC-130 gunship devastated the medical facility, Mr. Obama’s personal expression of regret in a telephone call from the Oval Office appeared to do little to satisfy the leader of the doctors group, who issued a terse statement saying the president’s apology had been “received.