Different forms of city government are in widespread use across the United States. The two most common structures are the mayor-council form and the council-manager form. In many large U.S. cities, there have been passionate movements to change the structure of city governments and equally intense efforts to defend an existing structure. Charter change (or preservation) is supported to solve problems such as legislative gridlock, corruption, weak executive leadership, short-range policies, or ineffective delivery of services. Some of these cities changed their form of government through referendum while other cities chose to retain the form in use.