Looking at what some former presidents (Jimmy Carter and Bill Clinton come to mind) say after they left, it seems that this change is not permanent. It's almost like moving into the White House makes folks automatons void of any previously held principles. And moving out makes them decent people again.
The fact is, there is a machine that exists beyond any sitting president, and that machine is adept at getting its way. Convincing one person, who does not have any former experience in these matters, that your way is the right way, is probably the easiest part of their job.
Why do you believe this? Is it entirely due to the "secret information" theory, where the President is sat down his first day and told all the skary sekrit stuff?