The point of the piece is Trump's hypocrisy. He said that only guilty people take the fifth, and then goes and takes the fifth.

As it is hard to keep track of the cases against Trump, the case mentioned is about how Trump over inflated the value of his real estate holdings when applying for bank loans, and then at the same time undervalued them when it came to paying his property taxes. He very likely will be convicted for tax fraud in New York.

Personally, I think Trump is an idiot, as someone who is committing tax fraud should never go into politics when his finances would be more closely scrutinized, making it much more likely he would get caught.

At this point it is just a question of can he buy his way out of it via political donations, or not.