Analysis: America's immigrants make it strong
The Obama administration has criticised the law, church groups have protested that it is discriminatory, and a federal court has issued a temporary injunction, ruling immigration is a federal issue. Regardless of the outcome of the legal case, the Arizona law has proven to be popular in other states.
If the US turned inward and seriously curtailed immigration, there would be serious consequences for America's position in the world. With its current levels of immigration, America is one of the few developed countries that may avoid demographic decline and keep its share of world population, but this might change if public xenophobia closed the borders.
Fears over the effect of immigration on national values and on a coherent sense of American identity have existed since the nation's early years. The 19th-century "Know Nothing" Party was built upon opposition to immigrants, particularly the Irish. Asians were singled out for exclusion from 1882 onward, and, with the Immigration Restriction Act of 1924, the influx of immigrants slowed for four decades.
During the 20th century, the nation recorded its highest percentage of foreign-born residents in 1910 - 14.7 per cent of the population. Today, 11.7 per cent of US residents are foreign born.
Despite being a nation of immigrants, more Americans are sceptical about immigration than are sympathetic to it. Depending on the poll, either a plurality or majority wants fewer immigrants.
Both the numbers and origins of the new immigrants have caused concerns about immigration's effects on American culture. Data from the 2000 census show a soaring Hispanic population. Indeed, demographers predict that in 2050 non-Hispanic whites will be only a slim majority of US residents.
Most of the evidence suggests the latest immigrants are assimilating at least as quickly as their predecessors.
While too rapid a rate of immigration can cause social problems, proponents argue that, over the long term, immigration strengthens the power of the US. Indeed, 83 countries and territories, including most developed countries, currently have fertility rates below the level necessary to maintain a constant population level.
By contrast, the US remains a country of immigration. The Census Bureau projects that the American population will grow 49 per cent over the next four decades.
Today the US is the world's third most populous country; 50 years from now it is still likely to be third (after only China and India). Not only is immigration relevant to economic power, but, given that nearly all developed countries are aging and face a burden of providing for older generations, it could help reduce the sharpness of the policy problem.
In addition, even though studies suggest the short-term, directly measurable economic benefits at the national level are relatively small, and unskilled workers may suffer from competition, skilled immigrants can be important to particular economic sectors. A 1 per cent increase in the number of immigrant college graduates leads to a six per cent increase in patents per capita.
While one can understand the resistance of ordinary American citizens to competition from foreign immigrants during a period of high unemployment, it would be ironic if the current debate were to lead to policies that cut the US off from one of it unique sources of strength.
• Joseph Nye, a former US Assistant Secretary of Defence, is a professor at Harvard and author of Soft Power: the Means to Success in World Politics.