Report: Mueller threatens Trump lawyers with subpoena?

So the most recent buzz is that Special Counsel has suggested to Trump's legal team that if the President refuses to sit down with investigators and answer their questions, that Mueller could (or that he would) "issue a subpoena" to force Trump to testify before a Grand Jury. The most likely outcome to a subpoena to force the President to testify would be a prolonged court fight. The least likely outcome to a subpoena to force the President to testify would be acquiescence.

To review the situation here, let's remember that this case appears to be the mirror image of the Clinton investigation. Whereas Clinton objectively broke the letter of the law with several of her actions, she was non-the-less provided a legal pass because the powers to be determined that there was no "intent" to harm anyone. On the flip side, Trump has not objectively broken any laws with any of his actions, but there is much speculation that the powers to be are trying to argue that his legal actions could be "illegal" because of some sort of criminal intent.

Given that as the background for the questioning, and given that the President is being cited as a "subject" of an investigation, it seems clear that the intention of such an interview would be to determine if investigators can tie together (from his testimony) some proof of nefarious intent, which would then allow them to possibly move him from "subject" to "target" or even recommend some sort of criminal charge (whether that be through an indictment or recommendation of impeachment).

Under normal circumstance, a criminal suspect cannot be subpoenaed to testify in regards to their own criminal case. Under normal circumstances only a witness to someone else's crime can be forced by subpoena to testify. But of course, Trump is not a criminal suspect (or a criminal target) and that is where the laws become sort of murky.

Under Grand Jury rules, Mueller could subpoena the President to testify before a Grand Jury, but the President would still maintain full fifth amendment rights against self incrimination. Given that much of questioning would be specifically to get the President to somehow testify against himself, it seems obvious that the President would not be constitutionally required to answer a lion's share of the questions. The very intent of the line of questioning Mueller is looking to take, makes whatever answers the President gives possibly "incriminating" because they would rely on someone's  interpretation of those answers. Which, of course, becomes a serious problem whenever you attempt to turn perfectly legal actions into criminal actions, based on some degree of "intent".

So even if the President considered himself completely innocent, he could still invoke the 5th amendment right, based on a fair belief that his answers could be use by Special Counsel to bring possible recommendations of charges.

Now given that Grand Juries are by nature secret, and closed to the public, there would be no good reason for anyone to ever "know" whether or not a witness (even the President) pleaded the fifth. But obviously as a matter of potential leaks, the President would prefer "not" to plead the fifth for optics sake. The preference would be to argue executive privilege for anything that is a part of what he does (or can do as President). He could argue executive privilege as it pertains to the firing of James Comey, he could argue executive privilege as it pertains to any conversations with subordinates, as well as arguing executive privilege as it pertains to any possible Presidential Pardons.

So given the extraordinary nature of this situation, such a subpoena would be ripe for legal challenges that a normal Grand Jury subpoena would not be. I will be curious how certain legal experts see this shaking out, and to some degree I will withhold full judgement till I gather those opinions. But it's clear to me that this situation may escalate fairly quickly and we just may see such a court fight.