With an election looming, no investigation can be deemed impartial, because every current public servant is likely looking for work in the next adminstration. Only someone that cannot hold office in the next administration can provide an unbiased determination.
A Special Prosecutor should be appointed under the stipulation that they will not be eligible to hold any federal office for five years.
Furthermore, a separate Special Prosecutor should be named for each alleged offense to ensure no one person can be improperly influenced.
Lastly, a Special Prosecutor per alleged infraction of federal law is critical because it will out-pace the abilities of any one entity to coerce an individual and the overall investigation.
Impartiality is critical to move forward as one nation.