It is often said that America is “a nation of immigrants.” But that’s not true in the strictest sense. As of the 2010 Census, the foreign-born share of the U.S. population was 12.9 percent, and so 87.1 percent of Americans that year were native-born non-immigrants. Granted, the nation of immigrants line tends to be used figuratively, to indicate that virtually all Americans come from somewhere else if you go back far enough. That includes the members of the indigenous communities that had settled in what is now the United States many centuries ago, and the descendants of the enslaved Africans who were brought to the Americas against their will. Yet when we use nation of immigrants so loosely, it loses all meaning.

And when you compare the foreign-born share of the U.S. population to other countries, you soon realize that while the absolute number of immigrants living in the U.S. is very large, we’re nowhere near countries like tiny Qatar, where over three-quarters of the population consists of foreign-born individuals, most of whom are guest workers, or Canada, where the foreign-born share is a robust 20.6 percent. The U.S. is roughly in the same ballpark as countries like Germany and Sweden, which have become major destinations for immigrants only in recent decades.

So what would it mean for America’s foreign-born population to dramatically increase in the coming decades? That is the question we ought to be asking ourselves in light of the new Congressional Budget Office analysis of the Senate immigration bill. At first, many observers focused on CBO projecting that because the Senate immigration bill will tend to increase the U.S. working-age population while not increasing the number of retirees, at least not yet, it will tend to increase economic growth, raise tax revenues, and cut the deficit. Over the first decade, the CBO projects that deficits will decrease by $200 billion relative to the current law baseline, while they will decrease by $700 billion over the second decade.

Advocates of the Senate immigration bill suggest that the CBO analysis thus demolishes the economic case against this particular version of comprehensive immigration reform, but of course the CBO is relying, as it must, on a series of assumptions that might prove untenable.

For example, the Senate immigration bill bars unauthorized immigrants granted provisional status from access to a wide range of means-tested federal benefits. This is despite the fact that, as the Migration Policy Institute has documented, the unauthorized immigrant population is extremely poor, with 32 percent of unauthorized immigrant adults and 51 percent of unauthorized immigrant children living below the federal poverty level. An additional 30 percent of unauthorized immigrant adults and an additional 27 percent of unauthorized immigrant children live between 100 and 200 percent of the federal poverty level, incomes at which many U.S. households still depend on safety net programs. The fact that unauthorized immigrants and recent immigrants are not eligible for the Supplemental Nutrition Assistance Program (SNAP) is a big part of why the U.S. has a higher incidence of food insecurity than other rich countries. Moreover, a number of liberals and centrists have already raised alarm bells about the fact that the Senate immigration bill bars legalized immigrants from the subsidies for medical coverage created by the Affordable Care Act, not least because this will put enormous fiscal pressure on cities and states with large immigrant populations.