A reposting from 2016:
Four countries were expressly founded on the necessity of immigration – The United States, Canada, Australia and New Zealand. Immigration was essential to the cultures and economics of these countries from the start. Gary P. Freeman of the University of Texas wrote in 2010 that no single piece of postwar legislation, with the possible exception of the Medicare Act, has had a more profound effect on the United States than the 1965 immigration law.
In 1995, he explained why immigration policy in the U.S. is both elusive and expansionist. (“Modes of Immigration Polities in Liberal Democratic States”.) First, migration takes time to develop, starting small and isolated, and grows without the native born population grasping what is going on.
Then, the direct benefits of immigration go to few while the costs are diffused. In the 2010 article Freeman lists the primary beneficiaries: immigration lawyers, ethnic groups, high tech employers, universities, religious institutions, hospitals, nursing homes, the hospitality industry, construction, and labor intensive sectors like meat packing, chicken processing, textiles, agriculture, and low-skilled services such as housekeeping and landscaping. (“Can Comprehensive Immigration Reform Be Both Liberal and Democratic?”)
Immigration politics is heavily client-oriented, largely out of view and without extensive public debate. An example is Senator Jeff Sessions of Alabama, who per his website “committed to immigration reform that serves the national interest – not the special interests – and that curbs the unprecedented flow of immigration that is sapping the wages and job prospects of those living and working here today.” A subcommittee he shares has denied the Dept. of Labor power to better enforce prevailing wage standards for H-1B temporary worker applicants.
Further, In liberal democracies, nativist talk about immigrants is viewed as disreputable. Strong anti-immigration politicians are usually roundly criticized. Popular opinion is generally more restrictionist than organized political party positions. Per Freeman, the national political positions are ineffective and contradictory, seeking to accommodate as many as possible without forcing the issues. Thus, per Freeman, liberal democracies have an expansionist bias.
A reposting from 2016: