Legal experts say it’s odd that he emphasized the lack of an underlying, proven crime, given that’s not necessary for obstruction of justice.

“I think this is the weakest part of Attorney General Barr’s conclusions,” said Jessica Levinson, a professor at Loyola Law School in Los Angeles. “You do not need to prove an underlying crime to prove obstruction of justice. Martha Stewart is quite aware of this fact.”…

Barr’s argument is that the lack of an underlying crime suggests there’s less reason to believe Trump had a “corrupt intent” behind his actions regarding the investigation. But if you set aside collusion, there would seem to be plenty for Trump to want to cover up. Even if these proven and alleged crimes didn’t involve criminal activity by Trump personally, he would seem to have a clear interest in the outcomes of these investigations, both because of his sensitivity about the idea that Russia assisted him and because of the narrative it created of a president surrounded by corruption…

And the last point is that this is not a determination Barr necessarily needed to make. Justice Department guidelines say that a sitting president can’t be indicted, so as attorney general, Barr’s conclusions about Mueller’s report weren’t really needed. Congress is the ultimate arbiter here, through potential impeachment proceedings. The fact that Mueller opted not to make a specific recommendation on obstruction of justice may have convinced Barr to weigh in, but he could have just left it at Mueller opting not to accuse Trump of a crime.