From the Document: "The trade aspects of 'Brexit,' the expected withdrawal of the United Kingdom (UK) from the European Union (EU) on March 29, 2019, are of growing interest to Congress. The UK is a major U.S. trade partner, and uncertainty over Brexit presents commercial challenges for the nearly 43,000 U.S. companies exporting to the UK and for U.S. firms operating in the UK, including some 4,000 majority- owned subsidiaries (2016 data). Details about the future UK- EU trade relationship remain largely unknown, and it is uncertain when and to what extent the UK will regain control of its national trade policy-- a major objective for Brexit supporters. These factors directly shape prospects for a proposed bilateral U.S.- UK free trade agreement (FTA), supported by the Trump Administration and several Members of Congress."
CRS In Focus, IF11123
Congressional Research Service: https://crsreports.congress.gov/