Good read from Greg Sargent:

What’s more, it should be noted that this was more than merely a defense against charges that Trump had previously given to Democrats. It was a key argument Trump made to GOP primary voters: That he is uniquely qualified to bust up and reform our corrupt political system, because he is intimately familiar with how that corruption works — from the inside. At a GOP debate as recently as March, he said:

“These super PACs are a disaster, by the way, folks. Very corrupt….There is total control of the candidates, I know it better than anybody that probably ever lived….I know it so well because I was on both sides of it, I was on the other side all my life and I’ve always made large contributions. And frankly, I know the system better than anybody else, and I’m the only one up here that’s going to be able to fix that system, because that system is wrong.”

In other words, Trump’s argument was that he gets how badly the system is rigged against you by bought-and-paid-for politicians, because he has bought and paid for politicians himself. That actually was his explicit argument, and it was one he made repeatedly.