1. Opening a new investigation is something that US Attorney’s are inherently already resourced to do. Most (if not in a tiny jurisdiction) have hundreds of Assistant US Attorneys (federal prosecutors) each of whom has staff support, as well as the services of law enforcement agencies. A Special Counsel is called for in cases where there is a real or perceived conflict of interest, not due to resource constraints. I guess if you abstract far enough, you could say that everything is about resources (or personnel, or policy), but that would be beyond the range of being able to make useful distinctions anymore.
2. The US Attorneys are directly vested with power in the Constitution. Prosecutorial authority is vested in them directly, not through the Attorney General. Like the Supreme Court and the US Attorneys, The Attorney General’s office was also created in the Constitution, and established in the Judiciary Act of 1789, but not in a supervisory, or chain of command role over the US Attorneys. The Department of Justice was established much later. Like the Department of Education exercises influence over colleges through controlling various funds, DOJ can pressure US Attorneys. Also over the years, various legislation has given DOJ assorted roles and authorities to regulate the US Attorneys, such as through the publication of the US Attorneys’ Manual. What has remained however, is the independent authority (and duty) of the US Attorneys to prosecute crime.
The US Attorneys are not vested with independent power as a fourth branch of government, in the Constitution.
Prosecutorial authority is vested in them directly, not through the Attorney General. Like the Supreme Court and the US Attorneys, The Attorney General’s office was also created in the Constitution, and established in the Judiciary Act of 1789, but not in a supervisory, or chain of command role over the US Attorneys. The Department of Justice was established much later.
The US Attorneys are part of the Executive Branch and have always reported to the president, first directly, then indirectly through the Department of Treasurey and then indirectly up the DOJ chain. They currently report directly to the DAG.
They are part of the Executive Branch. They are not independent, nor philosophically should they ever be.