Democratic members of the Senate Judiciary Committee have sent a letter to Republican committee Chair Lindsey Graham to insist on the importance of bringing Robert Mueller before their committee. To demonstrate the importance, the Democratic senators have included a list of 60 questions that can only be answered by the special counsel’s appearance.

The letter—which includes the signatures of 2020 presidential candidates Cory Booker, Amy Klobuchar, and Kamala Harris—shows there’s more to be learned from Mueller than can possibly be addressed in a single-page memo, including:

• To what degree was the investigation able to determine why Paul Manafort volunteered to work for the Trump campaign for free, and whether he discussed the possibility of joining the Trump campaign team with foreign nationals?
• To what degree was the investigation able to determine whether members of the campaign other than Rick Gates were aware that internal campaign strategy and polling data were being shared with Ukrainian Konstantin Kilimnik?
• To what degree did the investigation examine the role of Cambridge Analytica,
  AggregateIQ (AIQ), or SCL Group in the 2016 election? Did the investigation examine
  the possibility that U.S. election or Trump campaign information was shared with Russia
  through these entities?
• To what degree was the investigation able to determine whether the Trump Tower
  Moscow project was part of an effort to gain influence over Donald Trump?