Based on his prior position that Trump could not have obstructed ... even before he read the evidence. Not what was his opinion based on ... since it couldn't have been based on the evidence?
His opinion, which is shared by many legal heavyweights, is based on the Constitution. Barr is biased as to following the law.
He is also following the law regarding releasing the Mueller Report. The law which was passed by Dems and signed by a Dem President. But now, you're all for transparency, right?