POTUS administration hands are tied, for some reason.
It could be as simple as many have said, that the prosecutors and judges and staff are comped, and therefore no point in even pressing charges.
If you think about it, if the above is true, there is no way for Trump to do anything at all in terms of enforcing the law.
On the other hand, as a few have been arguing, why not start leaking out extraordinarily damaging information about the bad guys, to get the public's attention.