After all, what’s to stop Mueller from threatening to issue a subpoena compelling Trump’s appearance before the grand jury if he declines to submit to an interview? Even if Mueller should not do that, nothing says he could not do it. If he did, then Trump — despite the lack of just cause — would be put to an array of fraught choices — much to the delight, no doubt, of the Democratic partisans on Mueller’s staff. The president would have to (a) submit to questioning and risk that Mueller would decide his answers somehow incriminated him; (b) invoke executive privilege at the political cost of adversaries’ claiming he was concealing criminal misconduct or some kind of collusion with Russia; or (c) fire Mueller and risk comparisons to Watergate and calls for his impeachment — even though the Watergate special prosecutor had compelling evidence of President Nixon’s criminal culpability before demanding that the president submit to law-enforcement demands.

The answer to the “What’s to stop Mueller?” question should be obvious. It is the Justice Department. Alas, the answer eludes us because Deputy Attorney General Rod Rosenstein has been AWOL for seven months. We seem to have forgotten that Mueller answers to Rosenstein — and Rosenstein seems only too happy to have us forget.