Few issues dominate current American politics more than immigration. Images of migrants illegally crossing the southern border, and the detainment of those caught by the border patrol, animate both the Left and Right. Central to this debate is America’s large Hispanic and Latino population, mostly driven by decades of immigration from Mexico and Central America. (The terms “Hispanic” and “Latino” largely but not entirely overlap). The famous “melting pot” metaphor for assimilation has given way to more sectarian hopes by Democrats that the new arrivals will amplify their numbers, and to fears by Republicans that they will be outvoted. The hopes of the Left were perhaps most famously encapsulated in Ruy Teixeira and John B. Judis’s highly influential 2002 book, The Emerging Democratic Majority, which forecast a new progressive era largely based on demographic changes. On the Right, white Americans’ fears of becoming a minority in the coming decades helped propel Donald Trump into the White House. Yet from a certain standpoint, the influx of immigrants has changed America far less than imagined. One measure …