Speculate about this....

"Here's the real story, in my opinion, with Mueller's press conference: Mueller doesn't want to be called by Nadler to testify before the House Judiciary because he doesn't want to answer tough questions under oath. Nadler doesn't want to call Mueller because he doesn't want Mueller answering questions that undermine the Democrats' plan to keep a cloud of suspicion floating over Trump until 2020. Mueller and Nadler are communicating because Nadler was pretending to negotiate a Mueller appearance before his committee. Basically, Nadler was like, "I need you to give me something if you don't want to be called to testify." And of course, Mueller was more than happy to hold a press conference where he could recapture his rightful status on all those prayer candles after failing to seal the deal against Trump with his report. I should mention that the Senate Republicans can call Mueller to testify, but I have little faith they will do that because they are sad, weak little men.

A compromise had to be made because the Democrats' planned narrative was derailed with Barr's cut-to-the-chase press conference. But this time, Mueller delivered for the Democrats by insinuating that his team could not charge Trump because of DoJ's regulations not to bring charges against a sitting president...but would have if not for the regulation."

As for that DOJ regulation not to bring charges against a sitting president, there's this....

"AG Barr testified under oath otherwise about the DoJ regulation. Barr said that Mueller told him three times it was not the case that the OLC regulation prevented him from bringing charges. I believe Barr, who made this assertion under oath, over Mueller, who does not want to make any statements under oath. There were also witnesses to this conversation. I wonder what they have to say."