Robert Mueller has said that the report is his testimony. The following imagines what Republicans might ask or say during Mr. Mueller’s testimony. They probably wont.
Mueller: One, the Special Prosecutor’s team chose not to make a traditional charge/decline-to-charge decision. The DoJ’s Office of Legal Council has ruled that a sitting president cannot be charged and the team accepted the reasoning behind this ruling. (p. 194.)
Republicans: However, you didn’t have to charge President Trump. You could just have found that he did commit obstruction of justice, then leave it to Congress to follow through. Impeachment is a constitutional process. Why didn’t you find this conclusion?
Mueller: Two, the team investigated the facts in order to document occasions where other people had committed obstruction of justice and to document cases where the President may have obstructed justice in order for him to be prosecuted after he leaves office. (pp. 194-195.)
Mueller: Three, the team chose NOT to apply the common legal standard to the evidence that might have led to a decision that the President had committed a crime. (p. 195.)
1) Why not? Such a finding would lead to impeachment by the House. See above.
2.) Or was that because he had not committed a crime?
Mueller: The Federal Government is a sieve, so news of a secret finding would leak. This would cast a shadow over the President’s ability to lead. (p. 195.)
Republicans: So has the Mueller Report cast a shadow over the President’s ability to lead?
Mueller: Four, the team can’t tell if President Trump obstructed justice or did not obstruct justice. (p. 195.)
Republicans (incautiously): Why is that?
Overarching factual issues. (pp. 201-202.)
Mueller: It could not be a typical obstruction case because it concerned the President.
Mueller: First, some of his actions were “facially lawful,” but he also had official powers that could influence other people’s conduct. (p. 201.)
Mueller: Second, obstruction usually is intended to cover-up another crime, but the team did not establish that the President had committed any crime. So the team had consider whether other motives inspired his actions.
Republicans: like punching back against what he believed to be an un-fair investigation?
Mueller: Third, the President often acted in full public view, rather than in secret. Still, this might have been meant to influence witnesses.
 Such people can be prosecuted immediately.