AP Images/J. Scott Applewhite F our years ago, the modern Tea Party seemed to emerge from nowhere, leaving journalists bewildered and the public with few reference points to understand seemingly spontaneous rallies by middle-class people seeking lower tax rates. A search for the phrase “tea party” in connection with “politics” in major newspapers yielded fewer than 100 mentions in 2008—and when the words did appear linked together, they suggested studied formality and decorum. The next year, they appeared more than 1,500 times, often connected to “protest demonstration.” But little was spontaneous about the new party. “Social movements that explicitly defend the interests of the rich and the almost-rich have been a recurring feature of American politics,” Isaac William Martin, a sociologist at the University of California, San Diego, reminds us in his new book, Rich People’s Movements: Grassroots Campaigns to Untax the One Percent . “Such movements shook the American polity before the...