Robert Mueller’s testimony Wednesday on Capitol Hill is sure to capture the nation. Mueller has said very little publicly about his two-year assignment investigating President Donald Trump and how Russia worked to benefit his 2016 presidential campaign. Now, he’s in the klieg lights.

Still, Mueller is a reluctant witness, appearing not because he wants to—he said in May his 448-page report “speaks for itself”—but because House Democrats want to press him about how he arrived at certain conclusions, and what more he might want to say about Trump and his campaign’s ties to Russia.