On Tuesday, former White House counsel Don McGahn declined once again to appear before the House Judiciary Committee, this time defying the committee’s subpoena to testify. The committee’s chairman, Jerry Nadler, vowed that he and his colleagues “will hear Mr. McGahn’s testimony, even if we have to go to court to secure it.”

Count me as skeptical that the courts will ultimately compel McGahn to testify. Nadler declared, categorically, that “when this Committee issues a subpoena—even to a senior presidential advisor—the witness must show up,” but he has simply no basis for that confident legal opinion. No court has ever held that all presidential advisors must testify when subpoenaed. The closest thing Nadler can claim for precedent is a single federal judge’s decision in 2007, a decision that (like all trial-court decisions) is not a binding precedent. Indeed, in that case, the trial judge’s novel opinion never actually went into effect; the D.C. Circuit promptly blocked the judge’s decision pending further proceedings, before the entire dispute was extinguished by a voluntary settlement among the parties days before the next presidential administration.

In fact, the White House has the better of this argument, for all of the reasons set forth thoroughly in an opinion memo issued Monday by the Justice Department’s Office of Legal Counsel. As OLC explained, the president’s core advisors are entitled to absolute immunity from compelled appearances before Congress; they are his alter egos, and just as Congress cannot force the president himself to testify before its committees, nor can Congress force his closest advisors to appear. Such compelled testimony would subjugate the president to Congress; it would significantly impair (if not destroy altogether) the president’s ability to receive candid advice from his closest advisors, and it would enable congressional committees to prevent the president’s advisors from actually doing their own work for the president.

The memo draws on nearly four decades of consistent analysis by the Justice Department, including more than a dozen opinions over the course of eight Administrations. The memo is nuanced—indeed, it goes out of its way to caution that President Trump’s cabinet secretaries would not necessarily enjoy the same degree of testimonial immunity, because their offices “are created by acts of Congress,” their appointments “require the Senate’s advice and consent,” and their “responsibilities entail the administration of federal statutes.” The OLC made clear, “[t]hose officers can and do testify before Congress.” But the president’s close White House advisors need not. If McGahn had ignored the president’s instructions and volunteered to testify, he may well have been free to do so. But his choice not to testify is protected by the best reading there is of our Constitution’s principles and ramifications.

Nadler complains that McGahn sat for extensive interviews with Special Counsel Mueller, and provided extensive testimony recounted in Mueller’s final report. Others have argued, more directly, that McGahn “waived” his testimonial privilege by speaking with Mueller. But this misses the entire point of the testimonial privilege, which is to protect the presidency from being inappropriately subjugated by Congress. Special Counsel Mueller was part of the Justice Department—he enjoyed an important measure of independence from day-to-day management by the Attorney General, needless to say, but he ultimately was part of DOJ, accountable to its rules, and accountable ultimately to the (then-acting) Attorney General and even the president himself. Special Counsel Mueller did not work for Congress.

That is the most revealing part of the post-Mueller-Report controversies. In statement after statement, House Democrats seem to think that Special Counsel Mueller was effectively their private investigator rather than a Justice Department prosecutor. This is a profound mistake, as was the related mistake of Congress outsourcing its oversight responsibilities to the Special Counsel in the first place. The current House Democrats are not the first to confuse their powers with those of the Executive Branch or to mistake Justice Department officials for Congressional investigators. The upcoming rounds of litigation may prove to be an important civics lesson in that respect—a reminder that congressional oversight of the executive branch differs profoundly from the executive branch’s own internal self-policing.

Congress’s decades-long self-misunderstanding has only fueled the ever-escalating “criminalization” of political conflict. Congress has important oversight duties, rooted in its power to legislate, its power of the purse, its power to advise and consent (or not) to presidential appointments, and its ultimate power of impeachment. It should carry out that oversight publicly and energetically in the public arena. But too often, Congress has tried to turn its oversight into the stuff of criminal investigation; claiming the powers of federal prosecutors yet disclaiming traditional limitations and self-limitations that legitimize the use of prosecutorial power.

The irony in all of this is that, even though it claims broad oversight powers, Congress is effectively narrowing the nature of its inquiry into legalistic arguments befitting a prosecutor’s office rather than Congress. Its members have chosen to engage in arguments over whether the president broke the law by committing acts that meet the nuanced technical legal definition of “obstruction of justice,” instead of arguing that the president simply “obstructed justice” in a non-legalistic (and thus non-criminal) but politically salient way.

Having tried to outsource its oversight responsibilities to a Justice Department official, the House of Representatives will next try to outsource their oversight responsibilities to a district court, then a federal court of appeals, and perhaps even the U.S. Supreme Court (yet another tendency that is itself, unfortunately, not unprecedented). Having already tied its fortunes to a Justice Department special counsel, the House will next hope for the deus ex machina of a federal trial judge. This is an odd way to reassert Congress as the Constitution’s “first branch.”