Dershowitz contends none of that matters. So long as what the president is doing is allowed to him by Article II, his reasons—even his confessed reasons—do not matter.

It would be a violation of the separation of powers and the Constitution to charge a president with obstruction of justice for simply doing no more than exercising his constitutional authority regardless of what his motive is.

Let’s test that proposition.

Look back again at Dershowitz’s short list of things the president might do that could trigger an obstruction charge. The president, Dershowitz says, cannot destroy evidence. But wait: The very first sentence of Article II lodges in the president the “executive power of the United States.” One of those powers is the management and custody of presidential records. The 1978 Public Records Act seeks to limit that power by requiring the consent of the archivist of the United States to the destruction of records, in much the same way that the president’s power to initiate and halt criminal prosecutions is limited by the laws and rules governing the Department of Justice and the FBI.

Like the FBI director, the archivist has been expected to be above politics. But also like the FBI director, the archivist can be fired by the president.

Suppose Trump asked the current archivist of the United States—appointed by President Obama in 2009—to destroy certain records, as he asked James Comey not to investigate Michael Flynn. Suppose the archivist refused, as Comey refused. Suppose Trump then fired the archivist, as he fired Comey. Suppose Trump then told a television interviewer that he fired the archivist precisely because the archivist refused to destroy documents that might incriminate him—as he told Lester Holt that he fired Comey to shut down the Russia investigation.

If firing the FBI director to stop a prosecution falls within the president’s Article II powers, so then does firing the archivist to compel the destruction of documents. How then can Dershowitz insist that the president may not destroy evidence? By Dershowitz’s own reasoning, the president certainly can.

Indeed, under Dershowitz’s reasoning, the president can do a lot more than that! Imagine that a president has committed a wrongful act, one that could expose him to impeachment or other penalty. Imagine that there is one eyewitness to the wrongful acts, a military officer. In order to silence him, the president orders the officer into an action certain to lead to the officer’s death. Under Article II, the president is commander in chief of the armed forces. Can he then order military actions with the intent to eliminate inconvenient witnesses?

The Dershowitz answer would be “Yes.” And by his reasoning, his answer must remain on yes even after the president confessed to the whole business on television.