A lawyer for former White House counsel Don McGahn sent a letter to House Judiciary Chairman Jerry Nadler (D-N.Y.) Monday saying he won't testify before the House committee.Details: The letter was sent after the Trump administration said it told McGahn to defy a subpoena from the House Judiciary Committee and not testify at a scheduled hearing on Tuesday. What they're saying: "The House Judiciary Committee has issued a subpoena to try and force Mr. McGahn to testify again," White House press secretary Sarah Sanders said in a statement. "The Department of Justice has provided a legal opinion stating that, based on long-standing, bipartisan, and Constitutional precedent, the former Counsel to the President cannot be forced to give such testimony, and Mr. McGahn has been directed to act accordingly."Why it matters: The move is sure to infuriate top House Democrats investigating the administration. On Monday night, Nadler threatened to hold McGahn in contempt were he not to testify in Congress. McGahn was a key player in some of the most tumultuous episodes outlined in special counsel Robert Mueller's report, especially potential instances of obstruction of justice.The big picture: The White House instructed McGahn earlier this month not to provide documents requested under the House Judiciary's subpoena, later asserting executive privilege over the material. Go deeper: The other Don: McGahn is one of the Mueller report's biggest stars