Yet another White House staffer has defied a Congressional subpoena and has decided to forego showing up for Congressional testimony at the behest of Donald Trump. He was due to arrive at 9:00am. His lawyers notified Congress at 8:59am that he would not be showing up under the fictitious claim of "absolute immunity." (FYI: Absolute Immunity is not a thing.).
Mulvaney is a critical witness, as he has been implicated in testimony given by numerous witnesses already and he confessed to the crime on live television. Eventually he will have to testify. And when he does, it will be in the open.
The White House has blocked numerous people from testifying, including Don McGahn, Rick Perry, Rudy Giuliani and Charles Kupperman. Once public hearings start, the pressure will be on for these people to show up. And after the Articles of Impeachment are drawn up, they will be compelled to testify - in the open - and Donald Trump and Mike Pence will have to testify or plead the fifth.
Every witness that defies the subpoena just makes the case for an article of impeachment for Obstruction of Justice even stronger.