The growing number of Americans using federal food assistance, or food stamps, to get by has changed the way America's largest retailer, Walmart, does business. Walmart executives say that they are seeing a surge in shoppers at the stroke of midnight on the first of the month. That's when a number of states replenish the debit cards people who qualify for federal food assistance use. Nearly 46 million Americans or roughly 15 percent of the U.S. population rely on federal food assistance. Rock Center's Kate Snow previews her report on the growing number of Americans on food stamps airing this Monday at 10 p.m./9 p.m. CT.