In this week’s Republican presidential nomination debate, we can expect to hear more hard-line rhetoric about border fences and birthright citizenship. Regardless of who eventually wins in 2016, though, policy making on immigration in Washington will remain as paralyzed as it has been for a decade.But consider education, abortion, health care, gun control and marijuana. States blue and red are going their own way on all these issues, often in conflict with one another and sometimes in conflict with Washington. So why not let states decide how the foreign-born get to belong?It is already happening, and the only mystery is how much power over immigration will eventually devolve from Washington to the states.The Constitution gives Congress the sole power to determine “a uniform rule for naturalization.” The federal government gets to decide who comes into the country and how violators are sanctioned. But that actually leaves the states with a lot of room to maneuver.They can create a fragmented landscape of places that welcome the foreign-born and others that close their doors. And in living with a patchwork of rules, we might eventually end up with a federal policy that actually works.The great immigration challenge of our era is not at the borders but inside them. Whether newcomers and their children find opportunities to prosper determines the long-term success or failure of immigration. It’s not a matter of who gets in, but what happens to them once they’re here.Citizenship remains vital and singular, but there is growing variation in how it is lived from one state to another, even from one city to another. Given this wide variation of welcome and restriction, there are many degrees of belonging.Washington has epically failed in its duties to decide who gets papers, but the country has not fallen apart. The hard work of immigrant integration has been playing out in schools and neighborhoods, in cities and states.States differ in the access to health care and safety-net programs available to different categories of immigrants and their children. Dreamers, or unauthorized immigrants who arrived as children, are welcomed into public higher education in some states but shunned in others.Twelve states, the District of Columbia and Puerto Rico allow undocumented immigrants to obtain driver’s licenses. Twenty-two states demand electronic verification of work-eligibility documents for state agencies and contractors and, in some cases, private-sector workers.Much of this activity on immigration, both for openness and closure, has come in direct defiance of Washington. So many state and local law enforcement agencies refused to cooperate with Secure Communities, the federal program to coordinate local immigration checks, that it collapsed in 2014. Meanwhile, a lawsuit by 26 states has blocked implementation of President Obama’s executive action offering temporary haven to millions of unauthorized immigrants.The differences do not relate only to the undocumented immigrants. Some states make it easier for professionals trained abroad to get licenses; others make it harder. Some states create public-private partnerships designed to lure immigrants who hold investor visas. Others don’t bother.The decrepitude of the federal immigration system makes it necessary for states to go their own way. Across the West, cropsrotted for the second summer in a row this year because of a weekslong shutdown of visa processing for seasonal farm workers caused by State Department computer problems. The California Legislature is considering whether to grant work permits for unauthorized migrant farmworkers.Cross that threshold, and state-issued labor certification could be extended to other categories of immigrants. In effect, welcoming states could take immigration in the direction of medical marijuana, and license and regulate behaviors that are shown to work, in this case, even though they’re in violation of federal law.States with restrictive policies have been held back by the Supreme Court’s 2012 Arizona v. United States decision that struck down most of a law creating state offenses and state punishments for immigration violations. A president who supported a hard line on immigration could encourage states to again explore what’s permissible, with policies designed to create environments so hostile that the unauthorized move away.The divergence could grow so great that immigrants would choose to settle in welcoming places and avoid the unfriendly places. Even if it does not go that far, a period of vigorous experimentation by state and local governments would be more productive than the polemics and stalemate that characterize the federal debate.Public opinion surveys consistently find that substantial majorities of Americans think that immigration strengthens the country and should be either maintained at current levels or increased. Clear majorities favor a legal path to citizenship for the roughly 11 million unauthorized immigrants who live in this country. Those views will dominate when immigrants are judged not as boogeymen but as neighbors and co-workers, when policies are based on self-interest rather than populist harangues.To remain united, the United States can have only one form of citizenship. But states can compete over who gets access to the world’s best brains, to the people who will care for aging boomers and to young adults with years ahead of them to pay taxes and bear children.Americans and their marketplaces have a way of sorting these things out. Roberto Suro is a professor of public policy and journalism at the University of Southern California. (Curtsey: The New York Times)