You can bet the problems with the secret service in the white house START with the President, his staff and his family. How do they treat them? Dismissively? Arrogantly? Contemptuously? How long could someone be treated like that and not develop morale problems? How long before job performance would be affected?
Most of us have likely enjoyed awesome supervisors and would walk through fire if requested. They treated us well, cared about our lives, and worked through their management chains to ensure we would be recognized and gain more compensation. Why wouldn't we be devoted to a person who comports themselves that way?
Same thing with the Secret Service detail. They are likely very professional and stoic. Yet at the same time, when they have four bosses (a king, a queen, and two princesses...) that spit on them daily, have contempt for them, and consider the Secret Service a necessary evil...one can understand if perhaps the agents are vigilant 99% of the time instead of 100% of the time. They are likely weary of it all.