From the Washington Post story citing BuzzFeed:
Barr, who was previously attorney general under President George H.W. Bush, left little doubt about his views in an unsolicited memo addressed to the Justice Department last year. Made public by the Wall Street Journal in December, the 20-page document criticized Mueller for apparently focusing on actions that Barr claimed did not constitute obstruction, such as firing government employees.

But Barr was clear about what he called criminal obstruction in the “classic sense” — “sabotaging a proceeding’s truth-finding function." In his June 2018 memo, the attorney and member of the Republican Party laid out acts amounting to obstruction: “Thus, for example, if a President knowingly destroys or alters evidence, suborns perjury, or induces a witness to change testimony, or commits any act deliberately impairing the integrity or availability of evidence, then he, like anyone else, commits the crime of obstruction.”
It is ironic that William Barr would make that statement, since that is exactly what he counseled George Bush to do when he was last Attorney general. Barr is completely unsuited to be Attorney General because he, himself, suborned obstruction by advising Bush to pardon the Iran-contra conspirators on his way out of office. That meets Barr's own definition of obstruction! Bush could/should have been prosecuted for that abuse of power, since he had already been implicated in the conspiracy. Although I genuinely liked and respected the elder Bush, that final act was deeply offensive - and illegal. If Bush had been prosecuted, it would put a whole different face on the current peril we are in. Barr is directly responsible for Trump.