Neither the FBI nor the DOJ can investigate this without having a conflict of interest. Not sure how a special counsel or prosecutor could be appointed and investigate without the support of these two agencies. Especially since this involved the highest levels of not only the agencies, but the US GVT.
They’re dug in better than an Alabama tick.
I’m hoping beyond hope that President Trump and his team are carefully and methodically lining all the targets up, and when the subpoenas start flying, it will be truly be a most deplorable day!