"A State plainly could not arrest or imprison a President during his term of office, which would incapacitate the single officer in whom the executive power of the United States is vested," DOJ argues in the 2nd Circuit Trump tax return case. documentcloud.org/documents/6467… 
See if you think the case DOJ cites in support of this assertion has anything to do with the power of *states* to enforce their criminal laws. supreme.justia.com/cases/federal/…
The fact that DOJ finds no pertinent authority whatsoever to cite in this section--except for the OLC memo and something Robert Bork wrote during Watergate--amounts to the most eloquent refutation of the OLC memo and Bork's work during Watergate that I've yet seen.
An explainer: In my view, lawyers' memos to their clients--and that is what even the loftiest OLC memos are--should explain what the law is and what uncertainties there are in it, without polemic, based on authority you could cite in court to persuade a judge.
Legal memos that live up to that standard are useful because they provide the client--the person who actually has the power to make a decision--with a real sense of what discretion the law allows them and what is definitely allowed or forbidden.
What memos are not supposed to do is invent the law in uncertain areas as the lawyer wants it to be. There's a place for that in advocacy, but it's no help to the client to pretend in a memo that some rule you concocted is the last word. That could get the client into trouble.
The OLC conceives of its role as unique and exalted, as laying down "the law for the executive branch," and it is v influential--able to constrain what parts of the executive branch like the Department of Justice do by writing a memo. But there's less to that than meets the eye.
In pretty much the same way, the general counsel's office at Facebook can constrain what parts of Facebook do by writing a memo on a given subject, but that obviously doesn't make their opinions "the law" of the matter outside Facebook's walls.
So when you see a bunch of lawyers suddenly tumbled into a courtroom and asked to persuade a judge of something, it makes a very poor appearance for them to cite their own memos on the subject.
The memos ought to have set down for the clients (and later lawyers) what the *real authorities* are.
If it turns out the OLC memos on the president's immunity from prosecution don't contain any real authority that DOJ can cite in court--which is what seems to have happened here--then imo that shows that they're based on the memo writer pontificating about what ought to be.
And that would mean that OLC lawyers may have deprived their clients--federal prosecutors, in this case, who decide whether to bring cases before a grand jury--of the discretion to address serious wrongdoing by the president, without any basis in law.
