Why are his supporters convinced...
You could say this about all things Donald.
He is a professional con man. A flat out shyster. These realities are not even debating in any circles that include Trump from a business perspective (and social at that). Now, he's parlayed that into being an exceptional brand creator, entertainer and personality... and the three are somehow mashed into one consumable piece of plastic veneer nowadays to feed the reality TV hungry crowd.
He has them convinced, because selling #### to a bunch of suckers is, quite literally, Trumps greatest calling and claim to fame.
I'm not even saying this sarcastically, sardonically or even in a negative way... it's what he is. A personality that sells itself and somehow, he built a world brand by doing so. And did that by convincing people of some underlying value, often in the name itself - when in reality, there was no value there whatsover (Trump U, countless failed endeavors, but Trump the brand came through untarnished, and that's because of Trump, himself).
Now, you want that for reality TV and the dumb ### suckers who bought his books, classes, steaks, chinese made ties, fine. But not for ###### president, people.
Problem is, Trump's greatest asset is convincing people how great he is and that's why he can win... but this time, not just those suckers listed above are going to feel the pain of his history of failure, lies and fraud. And from a NYer who has witnessed Trump and knows people in circles with him, y'all are being played for suckers.