In the politics of the United States, elections are held for government officials at the federal, state, and local levels. At the federal level, the nation's head of state, the president, is elected indirectly by the people of each state, through an Electoral College. Today, these electors almost always vote with the popular vote of their state. All members of the federal legislature, the Congress, are directly elected by the people of each state. There are many elected offices at state level, each state having at least an elective governor and legislature. There are also elected offices at the local level, in counties, cities, towns, townships, boroughs, and villages; as well as for special districts and school districts which may transcend county and municipal boundaries. The country's election system is highly decentralized. While the U.S. Constitution does set parameters for the election of federal officials, state law, not federal, regulates most aspects of elections in the U.S., including primary elections, the eligibility of voters (beyond the basic constitutional definition), the running of each state's electoral college, as well as the running of state and local elections. All elections—federal, state, and local—are administered by the individual states, with many aspects of the system's operations delegated to the county or local level. Under federal law, the general elections of the president and Congress occur on Election Day, the Tuesday after the first Monday of November. These federal general elections are held in even-numbered years, with presidential elections occurring every four years, and congressional elections occurring every two years. The general elections that are held two years after the presidential ones are referred to as the midterm elections. General elections for state and local offices are held at the discretion of the individual state and local governments, with many of these races coinciding with either presidential or midterm elections as a matter of convenience and cost saving, while other state and local races may occur during odd-numbered "off years". The date when primary elections for federal, state, and local races occur are also at the discretion of the individual state and local governments; presidential primaries in particular have historically been staggered between the states, beginning sometime in January or February, and ending about mid-June before the November general election. The restriction and extension of voting rights to different groups has been a contested process throughout United States history. The federal government has also