keep their questions sharp and targeted. >> reporter: overnight, after mueller's request for guidance, the justice department instructing he must remain within the boundaries of his public report, something mueller said he would do in may. >> the work speaks for itself. and the report is my testimony. >> reporter: but democrats blasting the new guidance. >> it's part of the ongoing cover up by the ad conspiracy between the trump campaign and russia, but made no determination about obstruction of justice. >> there is nothing there, and we're going to see that tomorrow. >> reporter: president trump today dismissing the hearing as an excuse by democrats to push for impeachment. >> we have the best economy in history, the best employment numbers in history. gee! let's impeach the president. i mean, you figure it. these people have gone totally crazy. >> reporter: and we are learning tonight mueller has requested that one of his closest deputies sit next to him. that deputy will be there to