Barr isn't the only attorney general to fall out of favor with the President.
The development is a massive blow to President Donald Trump, who has argued for months that Obama administration officials targeted Flynn as part of the Russian Federation investigation in an effort to undermine Trump before he took office.
U.S. Attorney General William Barr says the federal government's efforts to crack down on violent crime in Albuquerque and other U.S. cities is paying dividends.
Kerri Kupec, the Justice Department's top spokeswoman, had first revealed Bash's review in May, after Republican senators made public a declassified list of USA officials, including former vice president Joe Biden, who made requests that would ultimately reveal the name of Trump adviser Michael Flynn in intelligence documents in late 2016 and early 2017.
A Justice Department spokeswoman declined to comment.
Bash's findings, the Post noted, concluded that no wrongdoing occured.
According to the Post, Bash and his team reviewed unmasking practices as well as whether officials at the time improperly leaked information to reporters. It began as a spinoff of an investigation by John Durham, the US attorney for CT, into the origins of what became special counsel Robert Mueller's investigation of Russian interference in the 2016 presidential election. Barr has so far elected not to make them public.
It was not immediately clear why a public report about Bash's findings has not been made available by the Justice Department.
The Post reported that the Justice Department did not intend to release the results. "It's ridiculous. It's a disgrace", Mr Trump told Mr Kelly.
Brennan told NBC News that he was not interviewed by the prosecutor, U.S. Attorney John Bash of the Western District of Texas, or anyone else related to the investigation.
Then-acting director of national intelligence Richard Grenell had declassified and personally delivered the list to the Justice Department - his arrival captured by a pre-positioned Fox News camera - on the same day the Justice Department moved to drop criminal charges against Flynn.
Trump has praised and criticized Barr in previous interviews, and he has used the Justice Department as a cudgel to go after perceived political enemies.
It will also likely inflame tensions between Trump and Barr in the wake of earlier reports that Barr will not be able to deliver his findings in a separate investigation into the origins of the Russian Federation probe before the general election.