When former special counsel Robert Mueller testifies to the House Judiciary and Intelligence panels on Wednesday, there is bound to be a lot of dreary posturing by politicians. But we hope there will also be substantive questions and that they will be answered rather than stonewalled.

Sadly, if Mueller takes literally the guidance he requested and received from the Department of Justice, we will have to endure a tedious time, for he was instructed to stick to what was already published in his final report, which came out in March.

Still, one can hope.

Republicans will ask about the origins of the FBI investigation into the Trump campaign. The collusion narrative turned out to be false, so someone had to have made it up. Who was it, and what role did our intelligence services play in that elaborate and long-lived falsehood? It is anathema that the feds should spy on a presidential campaign without probable cause, but that's what appears to have happened. Mueller can and should shed light on this and former spy Christopher Steele's dodgy dossier.

Republicans should focus on three specific lines of inquiry. First, what information can Mueller provide, openly or in a classified forum, on the evidence which precipitated the FBI investigation? Second, whether there is any undeclared evidence of wrongdoing by Trump, or any compromising Russian material on him. When did Mueller know there had been no collusion with Russia, and why did he not make that clear as soon as possible?

Republicans and Democrats both should demand that Mueller explain with crystal clarity why he did not charge Trump with obstruction. Was it because there was insufficient or no evidence upon which to do so? Or was it only because of the view that a sitting president cannot be indicted?

House Judiciary Committee Chairman Jerry Nadler and Intelligence Committee Chairman Adam Schiff say there is evidence of impeachable conduct by Trump. If so, Mueller should explain why he did not report such conduct. Democrats should also push for specific instances when Trump or his top officials were thought to have engaged in deception, if any.

The free exercise of democracy requires that the public knows the answers to these questions. Mueller probably knows them. He ought to spill the beans.