READ IT: Bob Mueller's blistering letter to Bill Barr released just ahead of attorney general's Senate testimony
Special counsel Robert Mueller (left, via AFP/Saul Loeb) and AG nominee William Barr (right, via screengrab).

The Justice Department has issued a copy of the March 27 letter sent by special counsel Robert Mueller to Attorney General William Barr.

Mueller complained about the investigation summary Barr presented to the public, saying it "created confusion" and undermined the "central purpose" of the special counsel's appointment to investigate President Donald Trump's campaign ties to Russia.

Barr is scheduled to testify Wednesday morning before the Senate Judiciary Committee about Mueller's report, and the newly revealed letter he sent to the attorney general expressing his frustrations.