From what I can tell, DT was educated by old-school gangsters. New York. 60s & 70s. Construction. Later casinos. There was no-way he didn't run across the Mafia. I'm pretty sure I read that Mar-a-Lago used to be gangster owned. The clowns infiltrated and destroyed the Mafia and their networks in the 70s & 80s. Probably took out quite a few of DT's friends.
I don't think DT was ever in the same club as the rest of the crooks. He has a code and values and honor, the same way that the old-school Mafia had a code and values and honor before they were corrupted by drug money. I don't think DT was Mafia either. I think he's a true maverick who saw the corruption around him and realized that something had to be done before the whole world went to crap. Think boot on face forever.
There comes a point in life when you realize that no-one else is coming to the rescue and it has to be you. The approach from MI to join the Plan sealed it.