A White House demand that Bush administration political appointees in the Pentagon abide by new ethics rules may prompt three senior Air Force officials to vacate their positions by the end of the month, Inside the Air Force has learned. The appointees' departure will leave several holes in the service's senior leadership structure until the White House nominates replacements. Three assistant secretaries -- John Vonglis, Craig Duehring and Kevin Billings -- are expected to vacate their posts by April 30...