What might be the lasting legacy of the Nunes memo is how President Trump reacted to it. According to reports, Mr. Trump suggested “the memo might give him the justification to fire [the deputy attorney general, Rod Rosenstein] — something about which Trump has privately mused — or make other changes at the Justice Department, which he had complained was not sufficiently loyal to him.”

In fact, Mr. Trump’s approval of the release of the memo and his comments that releasing it could make it easier for him to fire Mr. Rosenstein could help Robert Mueller, the special counsel, prove that Mr. Trump fired James B. Comey, then the F.B.I. director, with a “corrupt” intent — in other words, the intent to wrongfully impede the administration of justice — as the law requires.

After all, Mr. Trump is now aware that he is under investigation for obstruction, and he knows that Mr. Comey said that Mr. Trump wanted “loyalty” from him. Mr. Mueller could argue that the president’s comments that Mr. Rosenstein was not “loyal” and his desire to fire Mr. Rosenstein suggest Mr. Trump’s unlawful intent when he fired Mr. Comey.