ROCHESTER, Minn. — The 91-year-old ruling emir of Kuwait arrived at Mayo Clinic after a setback following surgery at home less than a week earlier. Mayo declined to confirm details, but a four-engine U.S. Air Force C-17 flying hospital landed at Rochester at 10:08 a.m. after a 16-hour flight from Kuwait. Sheikh Sabah Al Ahmad Al Sabah’s underwent surgery at home on Sunday. The emir’s diagnosis was not discussed by the official Kuwaiti news agency, but his powers were assumed by the crown prince. In diplomatic circles there was speculation that the emir’s condition would set off a family power struggle. A government announcement regarding the Mayo treatment said: “We ask the Almighty to aid his recovery and sustain His Highness, who is healthy and well taken care of, and to protect him from all harm.”