The Threat: How the FBI Protects America in the Age of Terror and Trump by Andrew G. McCabe:
I am not aware of another president who has weighed in against ongoing criminal prosecutions in the overt, hostile, and unrelenting way that President Trump has. This is a breach of propriety and of historical norms. Presidents don’t weigh in on those things. They don’t try to tip the scales of justice for or against a particular defendant. In our system, intervention from the outside is not only considered inappropriate—it is inappropriate. It undermines the operation of a fair system of justice. It sows seeds of mistrust. President Obama was rightly castigated for a single offhand remark, when he said of the Clinton investigation that he thought there was nothing there. The political world exploded: Was he trying to telegraph something to investigators? Was he sending a coded message to the attorney general? It was not a smart thing to say, as Obama surely realized. And yet it was not even in the same universe as what President Trump does on a daily basis—casting doubt on the legitimacy of the prosecution of Paul Manafort, as he has done since June 2018, and calling the Mueller investigation a “witch hunt,” as he does all the time.
For an FBI agent, watching the president seek to interfere with the ordinary process of justice is especially galling—an affront to our constitutional system. The work of every agent at every waking moment is governed by intricate procedures whose aim is to ensure that every step taken is by the book. The process has to be fair and rigorous from start to finish—for the sake of subjects and for the sake of justice. It is a high-minded regime. The Bureau suffers lapses, of course, as any institution does, but the standards are taken very seriously.