"[Card`s] latest paper shows that cities with high rates of unskilled immigration have reported no offsetting shrinkage in the number of native-born laborers. "
Card is forgetting to look at the opportunity cost to American citizens. Immigrants don`t move to American cities with lousy economies, they follow the money to cities with growing economies. Those cities shouldn`t have "non-shrinking" numbers of Americans working in them, they should have growing numbers of native-born workers. But with mass immigration, the immigrants crowd out American citizens who would otherwise move there.
Then, when the economy turns down, the American citizens flee. That`s exactly what happened in California: for generations, American citizens moved to California for the good life, but the flood of illegal immigrants made that too expensive. Then, when the economy turned down in the mid-1990s, the natives fled to other states.