Even people who insist that real or hypothetical statutes could create some kind of magical law enforcement authority existing outside and above the executive branch — a view rejected by many liberal legal scholars, including Justice Elena Kagan, in the wake of Justice Scalia’s famous dissent in Morrison v. Olsen — have nothing to stand on here. The Mueller investigation did not even have a statutory basis — the old Ethics in Government Act of 1978 that established the constitutionally dubious vehicle for such investigations lapsed two decades ago. Instead it proceeded on the basis of Justice Department regulations dreamed up during the Clinton administration. This piece of toilet paper could have been ripped up and ignored at any time, just like any other memorandum or executive order or standing rule that has issued forth from a previous administration. President Obama was acting fully within the scope of his authority when he tossed out Don’t Ask, Don’t Tell; so was Trump when he threw out DACA. I happen to think that both of these decisions were bad, but that doesn’t make them illegal or unconstitutional.
None of this is meant to suggest that a president’s authority is truly limitless, much less that he is never be answerable to earthly justice. If a president were to commit a serious common-law offense — a murder, for example — he would almost certainly be impeached in the House of Representatives, removed from office by the Senate, and tried in the relevant state jurisdiction. The same would probably hold true for many federal crimes — though not, it would appear, those related to campaign finance law, which Trump indisputably violated in October 2016. This is the genius of the impeachment mechanism: It resolves the essential tension between presidential authority over federal law enforcement and the culpability of the man in whom that authority is vested by stripping him of the former.