The framers of the Constitution set up a system of representation for the United States, which although informed by the experiences of other republics, was different from them. Outside the U.S. today, the main system of representation in republics is the parliamentary system, which lacks separation between the executive and the legislative branch. Under a parliamentary system, the chief executive, usually called a prime minister, is a member of parliament, but the Constitution establishes the legislature and the executive as two independent, but closely connected, branches. Members of the U.S. Congress experience a fundamental tension between being a trustee for the interests of the people and being their delegate. They also must balance the demands of the district with the interest of the nation, as well as determining the appropriate level of political party loyalty.