(I'll try to ask this in as non-biased way as possible)
If an Attorney General is part of a corrupt administration, would he or she be able to quash any and all Federal investigations related to that corruption as a way of protecting that administration?
For example, William Barr has been widely criticized for what some see as his acting more as Donald Trump's personal defense lawyer than as "the people's lawyer". Concurrent with this is the news that Rudy Giuliani, one of Trump's actual personal lawyers, is under criminal investigation by Federal prosecutors from the Southern District of New York. Some view this as a possible threat to Mr Trump.
Is the SDNY free to pursue the cases they want or do they need approval of the AG? If the latter, is it possible that a corrupt AG can "shut down" a case if it threatens their special interests?