From the conclusion of Special Counsels, Independent Counsels, and Special Prosecutors: Legal Authority and Limitations on Independent Executive Investigations (R44857, Apr. 13, 2018):
Both Congress and the executive branch have employed a variety of means to establish independence for certain criminal investigations and prosecutions. The use of special prosecutors, independent counsels, and special counsels all have allowed for the investigation of executive branch misconduct. Nonetheless, efforts to provide independence for prosecutors from executive branch control often raise constitutional questions. In turn, proposals to statutorily protect a special counsel from removal thus raise important, but unresolved, constitutional questions about the separation of powers. As a general matter, simply insulating a future special counsel from removal except for specified reasons appears consistent with the Court’s opinion in Morrison. To the extent the current Court might depart from the functional reasoning of that case and apply a more formal approach to the question, however, such proposals might raise constitutional objections. Likewise, constitutional objections might arise against proposals aimed to insulate a special counsel in a manner beyond the framework approved in Morrison.