> There's a pretty big excluded middle between "We can say with authority that X obstructed" and "We can exonerate X of obstructing".

Mueller was following Justice Department policy - he can't even say he thought a crime was committed, despite mountains of evidence, because the department's policy is it will never prosecute the president, so they can't indict, and thus won't ever accuse.

The president could murder someone on live television and department policy would be to say "Doesn't look like anything to me."