1. The United States has a presidential system, and presidential elections are held every four years. The American presidential election system is complex and the process is long. The main procedures of the election include pre-selection, holding a national congress of all parties to determine the presidential candidate, presidential candidate election, national voters voting for the "elector", the establishment of an electoral college by the "elector" to formally elect the president and the inauguration ceremony of the elected president.

2. List of elected chairmen: