If you have a personal code of ethics, that is something you are LOYAL to, independently and outside of your loyalty to your duty for me, your boss (in this hypothetical).

Those who are sinful/amoral/unscrupulous lack this loyalty to an abstract concept and have only one discernible loyalty other than loyalty to me: their own self-interest.

Now we can see how Trump turns a glaring weakness, namely the INABILITY to understand or anticipate the behavior of someone loyal to a code or concept (e.g. suckers, losers), into a strength by winnowing his field of staff and allies to those driven solely and transparently by self-interest.