Oh come on. All executive appointees serve “at the pleasure of the president”, the term has been used for decades or longer. While the FBI certainly serves the rule of law, the director of the FBI is appointed by and serves at the pleasure of the president. Recall for example that Mr Clinton fired and replaced every US attorney in the country when he took office.
There’s plenty of smoke and there may very well be fire, but investigations are run by agents, and decisions to prosecute are made by the DOJ.
If you’re actually concerned about any potential charges, the decision to prosecute is made by the attorney general.