COLUMBUS, Ohio — It could have been a sense of irony that prompted Mitt Romney to choose the music for his grand entrance into the Landmark Aviation hangar, where about 10,000 supporters had been waiting for hours. As his plane rolled in, the first stirring strains of Aaron Copeland’s “Fanfare for the Common Man” sounded, and the crowd went wild. The anything-but-common candidate and his wife smilingly accepted the deafening accolades of the adoring fans.