From the Summary: "This report provides an overview of the funding appropriated for border barriers, based on data from CBP [U.S. Customs and Border Protection] and congressional documents, and a primer on the Trump Administration's efforts to enhance the funding for border barriers, with a brief discussion of the legislative and historical context of construction of barriers at the U.S-Mexico border. It concludes with a number of unanswered questions Congress may wish to explore as this debate continues. An appendix tracks barrier construction mileage on the U.S.-Mexico border by year."
CRS Report for Congress, R45888
Congressional Research Service: https://crsreports.congress.gov/