I have already called for President Trump to resign. The reason: his admission that he fired James Comey, the former FBI director, in order to derail the Russia investigation.

Yesterday, in a hearing before the Senate Select Committee on Intelligence, the witnesses were Adm. Michael S. Rogers, Director of the NSA, and Director of National Intelligence Daniel Coats. Senators of both parties asked both witnesses whether the President asked them to influence the FBI’s Russian investigation. Both witnesses refused to answer. It was also clear that there was no claim of executive privilege, and indeed, as Directer Coats said expressly, no legal basis for the refusal to answer.

We are in uncharted constitutional territory. If the two witnesses yesterday were refusing to testify because they were directed by the President or someone else in the Executive Branch to refuse to answer the oversight committee’s questions, they should resign in protest. If they decided on their own not to answer the questions, they should resign in shame.

I saw some hopeful signs yesterday that even the Republicans on the committee regarded the witnesses’ defiance as unacceptable. Let’s hope they follow through with meaningful action to compel the testimony they, and we, are entitled to hear.