United States of America is a constitutional federal republic, located in North America. Powers are constitutionally divided between the executive, legislative and judicial branches, and between the federal and state governments. The president heads the executive branch. The federal legislature—Congress— consists of a House of Representatives, members of which are elected from constituencies based on population, and a Senate, members of which are elected state-wide (two per state). The president is elected every four years and House members every two years. Senators serve a six-year term, with one-third elected at each congressional election. United States is the 2nd largest economy in the world (by GDP PPP) and is ranked 19th in terms of GDP per capita. United States is also the world’s largest importer of goods and services and is the world’s 2nd largest exporter. However, total external trade is only 14% of GDP. Around 53% of total exports are directed to just three markets (European Union, Canada and Mexico). However, it is China, which is supplying most good to the United States (accounting for 21% of total imports). The central bank, Federal Reserve System (FED), has no explicitly stated nominal anchor, but rather monitors various indicators in conducting monetary policy. The FED also maintains a free floating exchange rate regime. High public debt and persistent budget deficits, high corporate tax and political polarization are usually name among key weaknesses of the U.S. economy.