SUCCESSIVE governments have stood by as America became home to more than 11m unauthorised residents. If they were all in a single state it would be America's eighth-largest by population, just behind Ohio. Many of those foreigners arrived years ago, working hard and bringing up American children. But their families have enjoyed only provisional futures, overshadowed by the original sin of a parent or parents who arrived without the right papers. Barack Obama now plans to shield many of these immigrants from the threat of deportation. Among other changes, his instructions to immigration authorities will allow the undocumented parents of American citizens or legal residents to apply for work permits—provided those parents have been in the United States for five years or more.

Analysis by the Pew Research Centre suggests that about 4m undocumented immigrants are newly eligible for temporary protection under the president’s plan. Add together all those granted papers by new or existing relief programmes, and 48% of all America's unauthorised residents qualify. Mexican immigrants account for two-thirds of those who will be affected.

Mr Obama says he has acted because the country’s immigration system is broken. Many of those who until now have lived in fear of deportation are migrants who have been working in America for more than a decade: when they are removed, that often divides long-established families. The subject of deportation is shrouded in confusion, as well as anger. Mr Obama has been attacked from the left as a "deporter-in-chief" after presiding over large numbers of removals as president. In 2013 America removed 369,000 undocumented migrants, a nine-fold increase compared with 20 years ago. Critics on the right call those statistics dubious, because the definition of "deportation" was changed to include the expulsion of fresh border-crossers. Either way, right and left can surely agree that it is not possible to find and deport all 11m migrants in the country without papers: priorities must be chosen.

Republicans are up in arms, not just at Mr Obama’s use of executive actions to push through his plan, but also for giving would-be migrants another incentive to try and enter the country. Mr Obama accompanied his plan with promises to beef up border security even further. However useful they are politically, such pledges have diminishing returns. America already spends more on immigration enforcement than on the FBI, the Drug Enforcement Administration, US Marshals Service and the Bureau of Alcohol Tobacco, Firearms and Explosives combined. The states with the fastest growing unauthorised-immigrant population are New Jersey, Florida, Maryland, Pennsylvania and Virginia, none of them border states. Meanwhile, the illegal-immigrant population in California, New Mexico and Arizona has declined. In particular, migration from Mexico has fallen considerably from its peak almost a decade ago, thanks partly to stricter enforcement and partly to improving economic prospects south of the border.