But of course, having recordings five years (at the earliest) after Trump leaves office would do little to resolve the political controversy right now. However, the Watergate precedent indicates tapes (or even “tapes”) could be subpoenaed. Ordered to turn over tapes of the White House, Nixon asserted executive privilege. The D.C. District Court rejected that claim, and Nixon appealed to the Supreme Court.

He lost there, too. By an 8-0 margin—William Rehnquist, a former assistant attorney general, recused himself—the Court ruled that the White House had to comply with a subpoena in a criminal case:

Neither the doctrine of separation of powers nor the generalized need for confidentiality of high-level communications, without more, can sustain an absolute, unqualified Presidential privilege of immunity from judicial process under all circumstances… Although the courts will afford the utmost deference to Presidential acts in the performance of an Art[icle] II function ... when a claim of Presidential privilege as to materials subpoenaed for use in a criminal trial is based, as it is here, not on the ground that military or diplomatic secrets are implicated, but merely on the ground of a generalized interest in confidentiality, the President's generalized assertion of privilege must yield to the demonstrated, specific need for evidence in a pending criminal trial and the fundamental demands of due process of law in the fair administration of criminal justice.

Presumably, a congressional subpoena about a criminal matter would also succeed in a similar case, on the same grounds.

As my colleague Jeffrey Rosen wrote earlier this week, Nixon nearly provoked a genuine constitutional crisis. The president considered refusing to comply with a Supreme Court order to turn over the tapes.

HuffPost reports that the Senate Intelligence Committee is considering ways to get its hands on the hypothetical Trump tapes. What happens if the committee issues a subpoena for them? It needn’t necessarily have proof they exist. The White House would then have a few options. It could simply say that no tapes exist—which if true would make the administration look silly, and if false would constitute a crime. Or it could say that tapes exist but refuse to turn them over, and try to litigate. Then a Republican-dominated Supreme Court would have to take up the old precedent in United States v. Nixon. (In that case, for the record, five of the justices were nominated by GOP presidents, and three by Democrats.) If the Court affirmed the precedent, Trump would be faced with the same decision as Nixon about whether to comply.

Of course, whether or not the tapes exist remains a central question. The White House’s absolute refusal to discuss it is peculiar, and so is Trump’s tweet, which may very well have been tossed off unthinkingly by the president. At The Washington Post, Philip Bump argues that there are good reasons to believe that Trump recordings do exist.