I have told people and they do not believe that the president can recall any former retired member of the military to active duty. The big talk was that McCain may have had his commission reinstated to face a court martial for giving aid and comfort to ISIS.
“Retirees (those who spend at least 20 years in the military and draw retired pay) can be recalled to active duty for life. However, the policy established in DOD Directive 1352.1 - Management and Mobilization of Regular and Reserve Retired Military Members, makes the recall to active duty unlikely for those who have been retired for more than five years, and those over age 60.”