The W.H. counsel has cooperated extensively in Mueller's investigation, sharing detailed accounts about the episodes at the heart of the inquiry into whether Trump obstructed justice, including some that investigators wouldn't have learned of otherwise nyti.ms/2ONyPWZ
Mr. McGahn was also centrally involved in Mr. Trump’s attempts to fire the special counsel, Robert S. Mueller III, which investigators might not have discovered without him. 
Trump’s behavior has so exasperated Mr. McGahn that he has called the president “King Kong” behind his back, to connote his volcanic anger.
Remember this?
We also know Mueller has been interviewing the chief of staff to Don McGahn.
And how about those documents McGahn has locked in a safe.
If it's true that McGahn started cooperating with Mueller because he feared Trump was trying to set him up, then it's pretty plausible Mueller has a solid obstruction of justice case. Let's go, wait till the midterms, impeach Trump.
