Just for the sake of argument, could it be a case of Seller’s Remourse.
Which is sort of like buyer’s remorse, only in this case, the seller trades his integrity and moral authority.
Barr is one of the major proponents of the concept of the Unitary Executive, a conservative constitutional notion that posits a strong executive, presiding over the other two branches. This is in keeping with the steady drift of power toward the Executive over the course of time. Many historians caution, that pseudo authoritarian notions like this is how democracy dies.
Barr has been the enabling agent for Donald Trump. His skates through the Mueller investigation, and his repeated actions to run cover for Trump’s grab bag of scandals has enabled Trump to get away with blatant corruption, obstruction of justice, malfeasance, and possibly treason.
In fact, Donald Trump is the poster child for why the Unitary Executive is not only wrong, but extremely dangerous.
Maybe the scales are falling off Barr’s eyes.
Bear in mind, that I doubt it, but it’s a thought.