Immigration, protection of the United States’ borders and the labor force share a wound that has yet to heal.

Republican presidential candidates Mitt Romney and Rudy Giuliani attacked each other in the recent debate on the issue of illegal immigration.

Romney accused Giuliani of allowing his city to become a “sanctuary” for illegal immigrants. Giuliani said Romney has a “sanctuary mansion” because workers on his property were in the U.S. illegally.

Giuliani said he didn’t run a sanctuary city but it did have three exceptions, to allow children to go to schools, to allow illegal immigrants to report any crime or abuse against them and the third was to rely on the emergency care in hospitals. Also, he said his officials have submitted thousands of names of undocumented immigrants suspected of committing crimes to federal authorities, of which few have been deported.

In Romney’s defense, he said he hired a company to do work on his house and couldn’t be held responsible for checking the papers of each of its employees.

Then, Romney asked Giuliani whether he was suggesting that someone who hires a service has to check out individual workers, particularly those that might look different or have a funny accent, he said. “I don’t think that’s American.”

Well if Americans want the labor force in the U.S. to grow, immigration policies cannot be closed off.

The Congressional Budget Office (CBO) projects that as long as people continue to move to and remain in the United States to work, the foreign-born share of the labor force will continue to grow. However, presidential candidate Congressman Tom Tancredo mentioned in the recent Republican debate that he does not support opening U.S. borders to immigrants that will come into the labor force and do jobs that American will not do. “I reject the idea categorically that there are jobs no American will take,” he said.

According to the CBO, foreign-born workers accounted for about 15 percent of all workers in 2004 and more than half of the growth of the workforce during the previous decade. They hold a disproportionately large share of jobs that require very little education. Over one-third of all dishwashers, janitors, maids and cooks are foreign born. How would those jobs have been filled in the absence of the new immigrants? Some of the jobs can presumably be filled by other workers, however, employers might have to pay higher wages or find other ways of making their jobs more attractive.

Census Bureau projections prior to the 2000 census illustrate the potential importance of immigration. The Census Bureau’s staff assumed that net migration to the U.S. would average roughly 900,000 to 1 million per year through 2050. Based on that and other assumptions, they projected that the total U.S. population would increase by about 128 million people between 2000 and 2050. In the absence of any immigration or emigration during that 50-year period, the increase would be only about 54 million people.

Basically, about 60 percent of the projected population growth would come from new immigrants and their offspring.

Nearly all of the projected additions to the population associated with immigration are under age 65. Looking only at people ages 15 to 64, about 50 million of the projected 60 million increase in population in that age group would consist of new immigrants and their children. Hence the future labor force growth is likely to be largely the result of immigration.

So the very hard decisions regarding immigration policy, in particular: how many immigrants to admit, the criteria for entry and how to deal with unauthorized admissions are likely to shape the size, and composition of the U.S. labor force well into the future.