To a navy veteran, as I am, the term "bearing" refers to the ability to maintain yourself with a proper "bearing" while approaching your destination (or target) at a specific "bearing" using electronic equipment whose accuracy depends on "bearings."  To McCain (a retired navy aviator), the term "losing his bearings" could be a slam on his manliness, his vision, his mental faculties, his ability to command, and, finally, his age.  To me, the term would merely say "you're fricking crazy," but I'm not an egocentric, power-hungry, corrupt, manchurican candidate running for the most powerful political office in the world.