It means he didn't consider wire-tapping to be something that he wouldn't do. We consider certain things to be 'beneath us' (or ourselves to be 'above' doing these things), if we are too high class, too dignified, or too ethically pure. So, 'Even though he had trained as a chef, he was not above eating at McDonalds' or 'He hated animal cruelty, but wasn't above mugging old people for their social security checks.'