The American form of democracy is fundamentally based on a separation of powers. If POTUS actions cannot constitute obstruction because that would amount to him obstructing HIMSELF, and that he could, if he wished, terminate any inquiry, or even exercise his power to pardon if he so desired, including pardoning himself, then that places him, by definition, above the Judiciary branch of government and above the law. This violates the principle of separation of powers which provides a system of shared power known as Checks and Balances. Thus, the American form of democracy as we have known it since the founding of our country and as established in the Constitution would no longer exist. Also, if POTUS can, by extension, pardon himself of any high crimes and misdemeanors (in this case obstruction of justice), which is the only constitutional basis for impeachment, then the option of impeachment itself is called into question.

@Heraclitus Congress retains the power to impeach and remove the President for any reasons they like. It seems that many Democrats want to impeach Trump simply because he had the unmitigated gall the win the 2016 election.

@doug6352 Yes, you have a point that Congress ultimately decides what constitutes high crimes and misdemeanors since it is not specified in the Constitution. However, this is not posed as a question about Trump specifically, but about the constitutional precedent that is now being discussed. If, theoretically, a POTUS can preemptively pardon himself or herself of any high crimes and misdemeanors for which he or she may be impeached, how then would impeachment be valid, implemented, and executed? It becomes a constitutional paradox that can then only be settled...well, by force.

@Heraclitus The pardon power relates only to criminal law, not impeachment. You can get a 9-0 SCOTUS vote on that. Giuliani has been saying a lot of silly things lately, but he was a great mayor of NY. He reminds me of Harry Truman, who said silly things as an old man, but did a very good job as President.

@doug6352 Oh, yes I know, but obstruction of justice is criminal law. By force, I mean that Congress would likely ignore the pre-emptive pardon and initiate the impeachment trial, anyway. Then it becomes a question of whether or not the party of the POTUS (Republicans in this case) ALSO ignore the pardon and vote POTUS out of office, and their votes would be needed for a successful impeachment. Are you willing to bet on that? In fact, that would be exactly why POTUS might play the pardon card, in order to give his party the Constitutional excuse to not vote against him regardless of what he has done. This is only speculation, of course, and is not the way presidential impeachment has worked in the past, but then again, no POTUS has ever had the power to overrule the Judiciary and pardon himself before as a preemptive strike against possible impeachment. Whatever happens, it would be one hell of a constitutional crisis.