Mueller testimony will be important, but far more important are McGahn, Lewandowski and Donaldson. (and others)

If he indicted Trump, Barr would have said "that's against DoJ policy. And now, you have charged a man who does not get due process to clear his name - prejudicing the impeachment process ..." (which is BS but you know the GOP would pull something like that for PR)

Mueller was screwed whichever way he went.

Maddow made a pretty good case that DoJ policy is questionable here but that would just be another argument ...

that's unfolded so far. How could he possibly have been when I haven't? There's no chance that these nonsurprises have lead him to realize belatedly that whoops! he made a mistake. In a very imperfect situation, he chose the course he felt most likely to lead to needed resolution.

As for "pushing us toward constitutional crisis," we've been in that for a long time now. This would be headed for the Supreme Court no matter what Mueller did.

So Mueller punted the ball he couldn't carry further to congress. The general feeling seems to be that our house judiciary committee's actions are being taken with great deliberation, step by step, due diligence all the way, with the reactions of one person in particular in mind: Chief Justice Roberts.

Please note that Trump & co have committed genuine crimes as a direct result of the legal process closing in on them, none unanticipated.