Second, Barr’s letter leaves important questions unanswered concerning what then-candidate Donald Trump and his associates knew about Russian interference, and how they responded to Russian overtures to assist the campaign. While Barr’s letter states that the investigation did not establish that the campaign reached an agreement with the Russian government to take actions to impact the election in Trump’s favor, it reveals that the campaign did field “multiple offers from Russian-affiliated individuals to assist the Trump campaign.” Yet President Trump and others have repeatedly claimed that they had no contact with Russians, or knowledge that Russians were acting to assist his campaign. Moreover, the Trump campaign did not bring the Russian outreach to the attention of law enforcement but secretly allowed a foreign adversary’s assistance. Remarkably, after the release of the Barr letter — which makes it undeniable that the Russians were seeking to help the Trump campaign — the president still denies it. Why? Why was the Trump campaign willing to allow the help of one of the country’s foremost geopolitical adversaries rather than report the overtures to law enforcement? And, as importantly, does the role that the Russians played in his election have any bearing on Trump’s current approach toward Russia? Only by seeing the full Mueller report can Congress and the American people make an informed assessment.

Third, until the Mueller report is released by the attorney general, Congress and the American people will not be able to evaluate the president’s conduct with respect to obstruction of justice. Existing Justice Department policy prevents the criminal prosecution of a sitting president. The department’s institutional view is that a congressional hearing room, not a federal courtroom, is the proper forum for the evaluation of presidential misconduct. According to Barr’s letter, the Mueller report details evidence of potentially obstructive conduct, but it does not reveal what that evidence comprises. Until Congress is provided the full report, it cannot evaluate the seriousness of the evidence. And we, the American people, cannot make our own evaluation.