Ast, it isn't about legal or illegal, it is about whether someone who aspires to be President can get away with not paying taxes, politically speaking it should be a huge negative.
That said, Trump got the 'fuck you' anti-establishment vote, so that fits in with that.
Anyone watch Michael Moore's Trumpland? He is comparing Trump to a hand grenade thrown by the disenfranchised, they know he is going to fuck things up for the establishment and that is why they voted for him. So his negatives didn't matter. This election cycle is singularly unique.