"This is a group of extremists who have created a cult in our country.” Author and history professor Heather Cox Richardson uses her latest book to show how the Republican party went from libertarian-leaning to embracing Christian nationalism. The discontent that riles American politics was sown in the 1990s. The ascension of Rush Limbaugh and Bill O’Reilly made much of talk radio, especially in rural areas, the domain of conservative viewpoints. Heather Cox Richardson, an author and professor of 19th-century American history at Boston College, believes that, at the time, multiple factors contributed to the rise of American conservatism…