Politicians have to "work their way up" the system to progress. You have look the other way at indiscretions, and you end up taking money along the way to support your campaigns, and become part of the system. (Yes, I've seen this firsthand).

Trump came into the system without any of that baggage--he never "owed" anyone anything, and consequently he couldn't be "bought".

And that's why he's so villified by career politicians.... 

 I misread your working your way up line. I understand what you meant now.