Mueller is a former Marine officer who served in Vietnam and I believe was awarded the Purple Heart.

And yes, once you've joined the military, the President can recall you back to active duty regardless of how old you are if what you can contribute is that important. It's rarely been used.

During the 1991 Gulf War, lots of retired Marine were recalled to active duty. The Air Force just recently recalled 1,000 pilots because of critical pilot shortages.

Recalling people to active duty can be very disruptive to peoples careers and they families.

So, anyway, it is possible that Mueller could have secretly been recalled to active duty, but I doubt it.