U.S. Intelligence Community: Homeland Security Issues in the 116th Congress [Updated February 1, 2019] [open pdf - 124KB]
"Intelligence support of homeland security is a primary mission of the entire Intelligence Community (IC). In fulfilling this mission, changes to IC organization and process, since 9/11, have enabled more integrated and effective support than witnessed or envisioned since its inception. The terrorist attacks of 9/11 revealed how barriers between intelligence and law enforcement, which originally had been created to protect civil liberties, had become too rigid, thus preventing efficient, effective coordination against threats. In its final report, the Commission on Terrorist Attacks upon the United States (the '9/11 Commission') identified how these barriers contributed to degrading U.S. national security. The findings resulted in Congress and the executive branch enacting legislation and providing policies and regulations designed to enhance information sharing across the U.S. government."
CRS Insight, IN11031
Congressional Research Service: https://crsreports.congress.gov/