He's mad because Mueller is sniffing around his TAX Returns, (Condo's in Russia) and, as has been mentioned earlier, it's not just that he's not worth half of what he claims,
never was, (how do you accurately monetize the
BRAND of an egomaniac), it is instead his charitable giving which is also on par with the Clintons, donating used underwear to Goodwill, as a tax write-off.
This is a testament to his character and this is something he protects like most narcissist, do.
Oh wait, the IRS Audit, that's always worked before.