Suppose you are with Jeff Sessions (Rosenstein), Donald Trump, and Robert Mueller sitting in Trump's office the day before Mueller is appointed Special Counsel, this happened.
Nobody knows for sure what was discussed but suppose you need to find a way to properly investigate the people that spied on Trump's campaign without it being made to look political or like retribution by the Democrats and media?
You need the people appointing investigators and running the show to appear like they are not on Trump's side so that the Democrats or the media do not interfere with their efforts. This also while not alerting the people they are investigating. You do not yank the security clearances or fire the people being investigated yet.
You keep them on so they can be legally spied upon by intelligence and questioned by the IG.
When you are done with them you fire them with recommendations by the IG and Jeff Sessions and appoint a prosecutor (Durham) to look into the charges.
This almost goes unnoticed because the Dems and media are laser focused on Mueller.
Mueller hires lots of obviously partisan Democrats and gives them free reign to investigate Trump knowing there are no crimes. Democrats and media salivate over this daily, they just know Trump is done for now.
Next you continue a very public battle with Trump to show the media and bad actors that everything is Ok, Trump is definitely going down, that nobody in the DoJ is listening to Trump's crazy suggestions. Same with Mueller, Trump savages him regularly and makes fun of Sessions. Sessions leaves and Barr is appointed in his place. Mueller recommends no charges against Trump but leaves a little wishy washy wiggle room with Obstruction to show he is still against Trump.
Mueller now done after giving a very deliberately horribly weak presentation of his case to Congress Barr dismisses Obstruction as a legitimate charge against Trump.
Durham investigation continues and is independent and free of questionable influence, he was appointed by Sessions that Trump hates and made resign.
Durham brings down the bad actors with protection by Barr.
This is a small analysis with just some of what happened but it is a good overview of how a string operation is implemented by very smart and seasoned law enforcement.