The Trump Foundation is in a class by itself, as Donald Trump used foundation money to buy things for his own personal benefit, was caught by the IRS for doing this, and forced to backtrack the wrongdoing. Trump would also lie and say his foundation was funded by his own personal money, when it was funded by outside donors to the foundation.
As much as it pains me to say this, I feel like Donald Trump's defense in this case was valid. He's just an idiot. I think he genuinely didn't know that he couldn't use a charitable foundation to buy himself stuff, and I think that his business is structured in such a way that no lawyer or accountant was ever going to tell him. Trump has always surrounded himself with the ultimate YES-men, people who will flatter his vanity without any argument. I think he gets bad advice, and in this case no one told him he was committing tax fraud.
I mean if you still believe that Trump is some kind of super stable genius playing 3D chess, then sure you can fault him for tax evasion. But that's not the portrait I see. I see a 70 year old overweight white grandpa who is very set in ways and unlikely to listen to anybody about anything. His family has always been rich so he grew up believing that rules didn't apply to him (in business, in sex, etc) and now that he's President his confirmation bias is overwhelming. His twitter feed paints a picture of puppy dog, living moment to moment, without any forethought or memory of anything at all.
So yea, the Trump foundation is clearly fraudulent. But even the Clinton foundation, which has legitimately dispersed billions of dollars to worthy causes, exists in a fuzzy grey area of tax law where you can pay no taxes on your income that you donate to it, while retaining control of the donated assets. You can pay your children or relatives to work for the foundation, while avoiding the gift tax. And you can solicit outside donations to the foundation, which presents the opportunity for people or nations to attempt to curry favor with you by giving you money. It's legal, but still shady.