“It became an open secret that he was using painkillers in sufficient dosages to keep him standing through the two-hour debates,” write the authors of “Inside the Circus.”…

The authors imply that the painkillers may have led to a humorous incident before an October debate in New Hampshire when the “manager of a rival campaign” overheard Perry belting out the song “I’ve Been Working on the Railroad” while in the bathroom.

“Wondering who was making all the noise, the campaign manager turned his head and saw, to his surprise, the governor of Texas,” the book states. “Perry came down the row of about twenty urinals and stood companionably close by.

Allen and Thomas continue: “Nonplussed, the campaign manager made a hasty exit; as the bathroom door closed, he could hear Perry still merrily singing away: “I-I-I’ve been working on the ra-a-i-i-l-road, all-l-l the live-long day . . .”