Put all this together, and it’s actually hard to think of a simple answer to Detrow’s question that honors all of the various principles of which an aspiring president needs to be cognizant. The candidate cannot say anything that promises either to direct or encourage Trump’s prosecution or to prevent it. Any such promise, in either direction, involves a statement of political direction to law enforcement on a specific investigative matter of the type that must be anathema.

The candidate can and should promise to pick an attorney general in whom the public can repose confidence and to defer to the Justice Department on investigative matters, in general—but it’s very important not either to seek or to suggest that one will seek any kind of understanding with the attorney general as to how he or she will behave.

A presidential candidate should also neither promise to use nor promise not to use the pardon power with respect to Trump. Circumstances might reasonably call for either course, and it’s important to maintain flexibility on the subject for now.