His children are mature and very smart, they've been working with him in the business for awhile. He doesn't need to tell them how to invest or how to run it. They already know.
The daughter is supposed to be the brightest of them all,and the heir apparent.
Still,it's only a BLIND trust if you don't know who is managing it. The purpose of a blind trust is to insure political figures that get advance notice of government policies and insider information don't use that information for personal gain. That way every decision their administration makes isn't suspected of being insider dealing and profiting,and the legislation they write and sign isn't designed to benefit them instead of the country.
You can NOT trust a billionaire to ignore making profits on advance information. It goes against their nature. It's what made them billionaires.
Can you seriously suggest that The Donald would not give tips to his spawn about mergers,new tax laws,etc,etc,etc that would cause his empire to lose money? Remember,this is a man whose business model is bankruptcy,which means he is a bottom-feeding scavenger that doesn't care who he hurts as long as he profits.
