[Timesink]

Look- the Secret Service is the only federal agency in the Executive Branch that can give the President an order. They believed his life may have been in danger, and the safest place for him was on Air Force One.

While it's quite rare for a President to go against the recommendations of the Secret Service (and Bush obviously did not on 9/11), I don't think a President is legally bound to follow their orders.

[Lunatic Fringe]

Hehe- he may not be LEGALLY bound, but I don't believe any President can really do anything when 8 Servicemen grab you and put you on a plane.