But other opposition groups have been less influential, and so far, opposition has remained relatively muted compared to what it was in 2007. Meanwhile, supporters have assembled a wide and diverse coalition in support of the bill.
Several groups in that coalition criticized the Heritage report's assertions Monday, including an assumption that most newly legalized immigrants would remain in households that consume more government benefits than they pay in taxes, discounting the possibility that many of them would become upwardly mobile, move into higher tax brackets, pay more in taxes and use fewer services.
"It doesn't match what has happened in America," Barbour said.
Barbour was joined on a conference call by economist Douglas Holtz-Eakin, a former director of the Congressional Budget Office and chief economic adviser to Republican Sen. John McCain's 2008 presidential campaign who now heads the American Action Forum, a conservative public policy institute.
Holtz-Eakin dismissed the Heritage study, saying it failed to measure broader economic benefits from the legalization of a large new workforce and that 50 years is too long a time frame for an accurate assessment of the impact. Holtz-Eakin has conducted an analysis concluding that because of low U.S. birth rates, the economy and population will decline without immigration. An immigration overhaul, he said, would boost annual GDP growth by nearly a percentage point and reduce federal deficits by more than $2.5 trillion over 10 years.
"All that is absolutely absent from this study, which as a result is a narrow, incomplete look at the immigration reform issue and focuses, in what should be a benefit-cost analysis, almost exclusively on costs," Holtz-Eakin said.
The Libertarian-leaning Cato Institute also made experts available to criticize the study, which it derided ahead of time as "fatally flawed." House Budget Committee Chairman Paul Ryan, R-Wis., who's taking an increasingly visible role backing immigration legislation, weighed in with a statement saying, "The Congressional Budget Office has found that fixing our broken immigration system could help our economy grow. A proper accounting of immigration reform should take into account these dynamic effects."