What would happen if we put in immigration restrictions?

[Albus Dumbledore]

Presume that the ongoing rush towards recession actualizes and we get a bad recession. Naturally, we get populistic types whose beaming smiles and charisma provide an escape from bleak reality gaining influence in politics. Presume we have a coalition of the usual/unusual suspects(xenophobes, labor unions, greens(population increase isn't good for environments)) who manage to get restrictionism passed this year with the bill put into effect starting in 2009. Use something like the 1920s immigration restriction acts as a model for the bill(so the United States cuts off most immigration besides a small number of immigrants from the EU, first world east asia, Mexico and the Phillippines to allow for replacement level growth). Also presume this bill includes provisions for strong border enforcement. What happens to America if this stays in place for a long time?