Except Trump likely didn't pay what he legally owes - Everyone is focused on the consulting payment to Ivanka and the 70k for hairstyling, but those weren't the interesting things in the NY Times piece to this CPA.
His claimed abandonment loss on his casino business which resulted in his NOL carryback and $70 MM tax refund appears highly questionable. To take that loss, he had to really abandon his interests, but in the bankruptcy, he ended up receiving shares in the restructured business after he abandoned his interest. That's a problem and why the Joint Committee on Taxation hasn't officially approved his refund. That amount could come due at any time plus interest.
Another item which raised an eyebrow was treating their NY estate as an investment property when the family basically describes it as a second home in publicly available interviews. By doing this, he creates another set of questionable deductions. Additionally, I'm guessing the conservation easement on the property is complete bullshit as those deductions are ripe for abuse.
Trump has never seen a line he wouldn't cross and has zero morals or ethics. His income taxes are no different than the rest of his miserable piece of shit life.