There simply wasn't much Mueller could do but to simply put the onus back where it belongs and that's with Congress. His job is finished. What Congress does going forward is something it and it alone must decide. As we all know a sitting president cannot be indicted. But, he most definitely can be after he leaves office. And this is when the fun will begin. Can you imagine the firestorm if his successor is a Republican who pardons him? We're just in year two of what could be a decade long process. What we could end up with a another Nixon. As Gerald Ford pointed out by the time all the indictments, trials , sentences and appeals are heard Nixon would have likely have died before serving a day of his sentence.