Report of the Select Committee on Intelligence, United States Senate on Russian Active Measures Campaigns and Interference in the 2016 U.S. Election; Volume 5: Counterintelligence Threats and Vulnerabilities (Redacted) [open pdf - 50MB]
From the Findings: "The Committee found that the Russian government engaged in an aggressive, multifaceted effort to influence, or attempt to influence, the outcome of the 2016 presidential election. Parts of this effort are outlined in the Committee's earlier volumes on election security, social media, the Obama Administration's response to the threat, and the January 2017 Intelligence Community Assessment (ICA)."
S. Rept. II6-XX; Senate Report 116-XX
U.S. Senate Select Committee on Intelligence: https://www.intelligence.senate.gov/