There is only one rational explanation for this performance. Mueller wants Congress and the public to presume that if it were not for the OLC guidance, it is very likely that he would have charged the president with obstruction — maybe not an absolute certainty, but nearly so.
And then, just in case we were too dense to understand the nods and winks, Mueller took pains to emphasize that, in our constitutional system, it is up to Congress, not federal prosecutors, to address alleged misconduct by a sitting president.
Simple as 1 + 1 + 1 = 3. Likely felony obstruction, plus inability of prosecutors to indict, plus duty of Congress to deal with presidential criminality, equals: Impeachment is the only remedy, unless congressional Democrats are saying that Donald Trump is above the law. (Good luck, Speaker Pelosi, trying to pipe down your AOC wing, to say nothing of the 2020 primary contestants, after that one.)
This should not be a surprise. We have been saying since shortly after Mueller was appointed that his investigation was not a collusion probe but an obstruction probe, and that this necessarily made it an impeachment probe.
Competing Views of Obstruction
As noted above, the apparent contradiction between Mueller and Barr is clarified by the timeline.
To grasp this, you must first understand that Mueller and his staff are completely result-oriented. If you’ve decided to act as counsel to a congressional impeachment inquiry rather than as a federal prosecutor, the objective is to get your evidence in front of Congress, with the patina of felony obstruction.
In the Nixon and Clinton situations, the rationale for impeachment was obstruction of justice. Significantly, the issue in impeachment cases is abuse of power, not courtroom guilt. Consequently, unlike a prosecutor, a counsel to a congressional impeachment committee does not need evidence strong enough to support a criminal indictment; just something reasonably close to that, enough to enable a president’s congressional opposition to find unfitness for high office.
Once you understand that, it is easy to see what happened here.
Mueller’s staff, chockablock with progressive activists, has conceptions of executive power and obstruction that are saliently different from Barr’s (and from those of conservative legal analysts who subscribe to Justice Scalia’s views on unitary executive power).