reach this conclusion:
Mueller went through great lengths to obfuscate his intentions and understandably so. As special counsel, Mueller was assigned to make a legal decision, not a political one. Following the precedent set by the Office of Legal Counsel, Mueller has consistently maintained that even if he found enough evidence to charge Trump with acts of obstruction, he wouldn't charge a sitting president. But he refused to decide that "even if" question. His words today further indicate that he did believe Trump should have been brought up on obstruction charges otherwise, and his actions point towards his refusal to make a political decision by proxy and give Democrats the green light to initiate impeachment proceedings.
https://www.washingtonexaminer.com/opinion/robert-mueller-probably-thinks-trump-obstructed-justice-but-refuses-to-be-democrats-impeachment-fall-guy