Barr’s position is indefensible. The Constitution gives the “the sole Power of Impeachment” to the House of Representatives, and the House Judiciary Committee has jurisdiction over impeachments. The Mueller investigation was, among other things, an investigation into possible criminal conduct by the president of the United States. There is no legal principle, including the separation of powers, that would permit the executive branch to block the results of an investigation into crimes allegedly committed by the president from the House of Representatives. To do so would deny the House’s ability to carry out its constitutional power of impeachment.
So why isn’t Barr being more forthcoming? The details contained in the report will not be as unwaveringly positive towards Trump as Barr’s four-page letter. As Barr notes, his letter was not a “summary” of the report and did not detail Mueller’s findings and analysis. While Barr provided the top-line conclusion that Mueller could not prove a conspiracy with Russia beyond a reasonable doubt, he did not detail incriminating evidence of potential coordination.