Which event is the focus of this diagram ?

The tea party movement is a. an official third party that challenges both democrats and republicans in national elections. b. an organized challenge to incumbents in the republican party by the most conservative wing of the republican party. c. an organized challenge to incumbents in the democratic party by the most liberal wing of the democratic party. d. an offspring of the green party that runs for state and local office in many midwestern states. e. the now defunct party that gave way to the republican party at the end of the “second party system.”