So, how is this supposed to play out?

Don McGahn, the former White House counsel, has emerged as the star witness in an upcoming House Judiciary Committee hearing that would examine whether Donald Trump obstructed justice during Robert Mueller’s tedious probe into alleged collusion with Russians who interfered in our 2016 presidential election.

But wait! The president is threatening to block McGahn’s testimony. He doesn’t want McGahn, who now is a private citizen, to speak to House lawmakers about what he knows. He won’t let him answer a couple of key questions: Did the president order him to fire Mueller? Did the president order staffers to lie about it?

Simple, yes? It sure is.

However, if the president succeeds in blocking McGahn from testifying under congressional subpoena, does that constitute an obstruction of justice?

Judiciary Committee Chairman Jerrold Nadler thinks it well could be a case of obstruction.

Hmm. In that case, there might be an impeachable offense in the making.