From the Introduction: "On October 16, 2018, the Trump Administration notified Congress, under Trade Promotion Authority (TPA), of its intent to enter into trade agreement negotiations with the United Kingdom (UK). Brexit--the withdrawal of the UK from the European Union (EU)--occurred on January 31, 2020. During the transition period, set to last until the end of 2020, the UK remains a member of the EU single market and customs union, and subject to EU rules. The UK and EU have launched negotiations on their future trade and economic relationship. Any final UK-EU agreement would directly inform prospects for the potential bilateral U.S.-UK free trade agreement (FTA)."
CRS In Focus, IF11123
Congressional Research Service: https://crsreports.congress.gov/