Here’s something technical but still worth thinking about: the issue with Trump is not the federal crime of “obstruction of justice” (which is defined by the federal statutes18 U.S.C. 1512 et. seq.) It is probably the case that the President cannot actually be criminally charged with a crime arising out of abuse of his or her Constitutional powers, if only for the practical reason that the President can fire any federal attorney who brings such charges and use his power over the DOJ to make sure a prosecutor who will drop the charges is assigned to the case. Also, there’s a possibility the federal courts would rule they have no jurisdiction over such acts as there is an argument that federal court jurisdiction over crime arising from abuse of official powers is pre-empted by the impeachment provisions in the Constitution.
The real issue is whether Trump is guilty of “high crimes and misdemeanors” (which as I have posted before is well defined by English common law as crimes arising out of breach of the public trust: abuse of power, failure to fulfill the legal duties of the office, corruption, treason, etc.)
Which means ultimately everything about Trump will depend on Congress. Mueller can report the facts and reach the legal conclusion or provide a prosecutorial opinion that Trump abused his power as President by obstructing justice but this will all be decided by Congress, not the courts.
So the real issue here is not the technical legal of “did the President obstruct justice” or “can the President commit obstruction of justice?” The real issue here is: did Trump abuse his power? If it is found that Trump used his Presidential powers to impede a lawful investigation into the wrongdoing or himself or those close to him, that IMO would be a text book example of abuse of power.
One of the specific reasons that the Constitution contains impeachment provisions was to avoid the “monarchial immunity” of the British royal system. Let me again go to the source, Federalist Papers 69 which says:
“The President of the United States would be liable to be impeached, tried, and, upon conviction of treason, bribery, or other high crimes or misdemeanors, removed from office; and would afterwards be liable to prosecution and punishment in the ordinary course of law. The person of the king of Great Britain is sacred and inviolable; there is no constitutional tribunal to which he is amenable; no punishment to which he can be subjected without involving the crisis of a national revolution. In this delicate and important circumstance of personal responsibility, the President of Confederated America would stand upon no better ground than a governor of New York, and upon worse ground than the governors of Maryland and Delaware.”
So it is very clear that a President can be impeached for abuse of power, which includes abusive use of legal powers.
This is one of those things where the legalistic framework around impeachment that arose during the Bill Clinton years creates confusion. The issue here is not statutory and technical; the issue here is abuse of power. And using your powers to impede an investigation into illegal conduct by yourself or those close to you is crystal clear abuse of power.
Edit: I was typing this while Malathor posted, which means I am essentially agreeing with Malathor on this narrow technical point.
The question is, what about abuse of power?