Last week the United States’ first major immigration reform bill in two decades collapsed in the Senate. Buried in the ongoing debate was the potential economic impact of a measure that could change the composition of America’s workforce in significant ways: By cracking down on illegal immigration the legislation could constrict the future supply of low-skilled workers while a move to skill-based visa evaluations could provide more workers for booming high-tech industries. Meanwhile it isn’t exactly clear what impact the country’s 12 million illegal residents have on its economy. Experts from Wharton and elsewhere weigh in.