It is part of the DOJ Manual which provides the operating rules for prosecutors - although not a rule binding upon the public under administrative rulemaking authority- if that helps you to do your crabwalk in any way......which it does not.
And my point stands: There is a DOJ departmental rule binding on prosecutors that says that a prosecutors will not indict a sitting president. Because it is a rule the department can change that but my point remains the same: ie. to try to indict Trump would just create another example where the DOJ set aside existing rules and policies to go after Trump. You can get away with it but it what it is if it is done. Another "HQ Special" and "Insurance Policy" suddenly made available just for Trump.
We're not, at least I'm not, talking about the DOJ prosecuting Trump
while he is President. That won't happen. What will happen is that Mueller will wait until after the mid-term and present his report to the New Congress in late January or February, unless of course his hand is forced before then.. This business about DOJ rules re the indictability of a president are only a curiosity there for the benefit of the President's bedtime reading and to help soothe him to sleep. The DOJ opinion has no impact here because the Congress will decide whether to impeach, and the Senate will decide whether to remove from office. If he is removed, the DOJ can then indict him (he is no longer president), or alternatively Mr. Pence could pardon him. It would take an independent Federal Prosecutor to indict a sitting President, and we don't have one in the present instance. This stuff about DOJ rules and opinions re 'can the President be indicted?' is moot. Of course the president can be indicted. After he is out of office by the DOJ, and while he is in office be an independent prosecutor, but not by the DOJ.
The DOJ's opinion seems to give weight to "The Unitary Executive" concept, suggesting that even an independent prosecutor could not indict a sitting president. But it is just a concept and opinion uncodified in law. The law, until a statutory law dealing with this subject is enacted, is silent. And that includes Constitutional law. There is nothing per se to bar a sitting president from being indicted, but there is something that would bar the DOJ from indicting a sitting President. That, however, has nothing to do with DOJ opinion or rules.
I would say that in both the question of whether a sitting President can be indicted or whether a sitting President can pardon himself, although the law is silent, "originalism" speaks clearly and loudly; To Wit: A sitting president can be indicted, but not by the DOJ; A sitting President can not pardon himself.*
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*I have not given any specific reasons other than indicating that these conclusions hark back to the original intent of the Founders, and to consideration of conflict of interest. It does not take a particularly clever person , however, to deduce the reasons by considering the intent of the Founders. Naturally, new statutory law could be used to counter the intentions of the Founders. I personally think that would be a bad idea. Something this fundamental should only be enacted by amending the Constitution. Let us hope that such an Amendment is never enacted.