Did Trump belittle Mueller with tweets, threaten his firing and generally complain out loud about Mueller and his investigation? You're damn straight he did...
Barr looked at the compiled evidence and determined there was no prosecutable obstruction. Mueller's inability to come to that same obvious conclusion is likely a result of his own hubris.... He thought he did a fine job, and Trumps tweets, threats and stinging criticisms obviously hit their target... Mueller's ego left him bitter towards the president and when you couple that with his inability to actually 'get' the president, he was left with one final chance to put it to the Donald.
His now infamous "I didn't exonerate the President speech." His final salvo before he slinks away to retirement, obscurity and critical scorn for his failure to come up with something impeachable and his failure to absolve Trump. Everybody hates Mueller. The exclamation point on his obituary... FAILURE!
But their goal was never indictment, it was impeachment. Just look at the Dems reaction to his 9 minute press conference and it should be clear that the fact that “there was no prosecutable obstruction” is irrelevant.
Like most progressives, Mueller was still a child at heart. Playing those childish games.