The debate in Washington over reforming America’s immigration laws has produced not only heated rhetoric but a few fantastic claims. Few are wilder than a prediction from a well-known think-tank that the reform bill just passed by the Senate will result in 103 million legal immigrants to the United States during the next 20 years.

In a “Web Memo” from the Heritage Foundation, author Robert Rector claims that the Hagel-Martinez immigration bill (S. 2611) would unleash a flood of chain migration that would overwhelm America’s capacity to absorb so many people. He calculates that the bill would not only allow in an ever escalating number of new temporary workers, but that almost all of them would eventually become citizens, enabling them to sponsor spouses, children, parents and even grown siblings to immigrate.

The headline number certainly generated buzz, but it flows from assumptions that don’t hold up to scrutiny. Its bottom-line number doesn’t even pass the laugh test.

To total 103 million legal immigrants over 20 years, immigration would need to average more than 5 million a year. During the past decade, legal and illegal immigration combined has averaged 1.5 million a year. Nobody who specializes in immigration believes current inflows will triple if even the most generous version of S. 2611 were to become law.

Immigration is fundamentally driven by demand in the U.S. economy for workers. When the economy picks up, so does the inflow of immigrants; when it slows, so does immigration. Even with the extension of the capital gains and dividend tax cuts, it is ludicrous to assume that the U.S. economy will grow enough to accommodate 5 million new immigrants each year. Whatever the provisions of an immigration bill, the number of new immigrants will be limited by the growth of the U.S. economy.

The Heritage study wrongly assumes that almost all temporary workers will become permanent and eventually citizens. This ignores the fact that Mexican migration has traditionally been circular, with most Mexican migrants eventually returning home.

It also wrongly assumes that the exaggerated numbers who become permanent will then sponsor large numbers of relatives to also immigrant permanently — so-called chain migration. Our own recent experience with legalization exposes the error of the Heritage Foundation’s estimates.

The 1986 Immigration Reform and Control Act (IRCA) legalized 2.7 million undocumented workers. In what was truly an amnesty, it offered immediate permanent legal status (i.e. a “green card”) to illegal workers who had been in the United States more than 5 years. Even this accelerated legalization program did not unleash anything like the wave of chain migration the Heritage paper predicts from the more incremental Senate bill.

In the 20 years since IRCA was enacted (by coincidence the same time frame as the Heritage study), the United States has accepted an average of 950,000 legal immigrants per year. When you subtract out the baseline annual immigration of 600,000 in the decade before IRCA, and the 2.7 million workers directly legalized by the IRCA amnesty, the annual increase since then amounts to less than 200,000 a year from pre-IRCA levels — or about 4 million over a 20-year period. And a significant share of that increase can be attributed to a 1990 immigration bill that raised quotas for legal immigration.

Obviously, the 1986 amnesty did not cause anything like a flood of chain migration. There is no reason to believe the Senate reform bill will either.

A far more credible and objective study just released by the Congressional Budget Office estimates that S. 2611 would increase the U.S. population by only 8 million in the first 10 years. Although more chain migration would be expected in the second decade after the original temporary workers achieve citizenship, the rate of 800,000 immigrants per year is far more in line with recent history and the expected need of the U.S. economy for new workers.

An analysis by President Bush’s Council of Economic Advisers exposed a number of flaws in the Heritage study. The CEA found that the study double counts millions of new immigrants, first as guest workers, then again as new green-card holders. It substantially overestimates the number of illegal immigrants who would remain in the United States permanently as well as the number of parents of newly naturalized citizens who would immigrate, and it ignores millions of immigrants would later choose to leave.

The kind of sensible, comprehensive legalization program supported by President Bush and now the Senate would not have the draconian effect on the federal budget or U.S. population that opponents are claiming. Indeed, by turning an illegal flow and population of immigrants into a legal flow and population, reform would secure our borders, reduce illegal immigration, invigorate our economy, and uphold our best values as a nation open to peaceful, hardworking immigrants.