This sad state of affairs is deeply at odds with the rule of law. Whatever else that concept means, it surely requires that ordinary people be able to readily determine what laws they are required to obey, and that whether or not you get charged by authorities depends more on objective legal rules than the exercise of official discretion. Unfortunately, neither holds true in the United States today.
...There is much to criticize in both Obama’s and Trump’s approaches to legal issues. But the problem goes well beyond the flaws of any particular politician. The real threat to the rule of law is inherent in the enormous scope of discretion possessed by the executive in a system where there are so many legal rules that almost everyone has violated some of them, and it is not possible for law enforcement to target more than a small fraction of the offenders.