I'm a bit worried DEMs are relying too much on Mueller testifying. He's a by the book type of guy and he's not going to make any assertions that aren't laid out in his report. If DEMs are hoping Mueller is going to say, "Impeach the Motherfucker", then that's just not going to happen. He's probably not going to give them any kind of useful soundbite on the matter. He'll probably verbalize that he was heavily guided by the OLC opinion/guidelines, so he might contradict Barr on that front but beyond I think Mueller is going to go out of his way to avoid making big news which isn't spelled out in the report.
Instead of Dems wasting their time trying to get Mueller to say inflammatory things, I hope they're smart and organize enough to ask targeted and follow-up questions, which allow Mueller to explain key aspects of his report in plain English. I also hope DEMs don't wash his balls and heap tons of praise on him, it'll just come off as partisan. Just be matter of fact and ask the questions. Save the praise for Nadler's opening statement and leave it at that. The Republicans will be doing their best to turn it into a partisan circus so the hearing can be easily dismissed, so just let the Republicans look like political hacks without giving them additional ammo.
Nadler's first big public hearing with Matt Whitaker was disaster, so hopefully he can keep things under better control this time. I just hope the DEMs on the committee understand the gravity of having Mueller testify and they actually prepare beyond some banal repetitive questions.