For some time, the question of obstruction revolved entirely around the true reasons for Mr. Comey’s firing. Mr. Trump’s lawyers have argued that the president was within his constitutional rights to fire Mr. Comey for any reason — and that, in any event, he had such a reason. They point to the controversy over Mr. Comey’s handling of the Clinton email investigation, and they stress that Deputy Attorney General Rod Rosenstein provided the president with a particularly damning memorandum making the case for the former director’s breach of departmental procedures and standards.

But none of these complexities are present in the Cohen, Manafort and Flynn cases. In those, the president and his agents may have simply sought to undermine lawful inquiries. It bears remembering that when the House Judiciary Committee voted articles of impeachment against Richard Nixon in 1974, Article 1 included a charge against him for lying to Congress. The impeachable conduct was defined to include “condoning” and “acquiescing in,” not only “approving” and “counseling,” false testimony.

The Cohen, Manafort and Flynn cases may reveal yet another instance of such impeachable, and perhaps prosecutable, acquiescence — if not more in the nature of “approving” and “counseling.”