For the $5.5 billion figure, the Republicans relied on 1990 figures provided by the Center for Immigration Studies.

The 'attrition through enforcement' doctrine is one that think tanks such as the Center for Immigration Studies have been supporting for several years.

The Center for Immigration Studies has also commented on the issue.

"This bill represented something so big that people noticed," said Mark Krikorian, executive director of the Center for Immigration Studies, a research group.

Another study, by Steven Camarota of the Center for Immigration Studies, reached similar conclusions.

According to the Center for Immigration Studies, immigration has been responsible for 70 percent of our country's population growth in the 1990's.

According to a 2012 survey by the Center for Immigration Studies, 16 states require use of E-Verify in some form.

Mark Krikorian, executive director of the Center for Immigration Studies, describes the study as a cartoon version of how enforcement would work.

The Center for Immigration Studies finds a 3.7% depression wages from immigration from 1980 to 2000.

The Center for Comparative Immigration Studies, 70.