Thursday’s report in The Times that President Trump ordered the firing of the special counsel Robert Mueller last June, only to back off after the White House counsel, Donald McGahn, threatened to resign, is explosive on many levels.

On the surface, the revelation is one more piece of damning evidence in the now-overwhelming case of obstruction of justice that Mr. Mueller has assembled. The core of the case — the Feb. 14 meeting in which Mr. Trump asked the director of the F.B.I., James Comey, to drop the investigation against the national security adviser, Michael Flynn; Mr. Trump’s subsequent sacking of Mr. Comey; and Mr. Trump’s serial lies about Mr. Comey’s firing — has long been solid. And Mr. Mueller has added significant pieces of circumstantial evidence, such as Mr. Trump’s apparent knowledge that Mr. Flynn had lied to the F.B.I. when he buttonholed Mr. Comey.

Thursday’s revelation seals the deal. The president’s attempted ouster of Mr. Mueller seems plainly to have been intended to squelch Mr. Mueller’s investigation. Moreover, Mr. Trump’s attempts to conceal the obvious with a rank, virtually comical explanation provide additional evidence of guilty intent. Mr. Mueller, the president argued, could not serve because, years before, he had resigned his membership at the Trump National Golf Club in Virginia because of a dispute over fees; or he needed to be fired because he had worked at the law firm that previously represented Mr. Trump’s son-in-law, Jared Kushner.

Why strain to concoct such feeble rationales unless the truth is indefensible?

Then there is the provocative point that Mr. Trump’s efforts were parried by the threat to resign of his own White House counsel, Mr. McGahn. White House counsels are not in the habit of bucking their bosses that way; it’s an extraordinarily rare event.