Walmart is reporting disappointing fourth-quarter profits and sales. The nation’s largest retailer said Tuesday that sales at its U.S. stores heading into the holiday season were weaker than expected. It also said that social unrest in Chile hurt its business. The company is reporting strong sales in grocery, helped by its expanded online delivery services. That helped to push same-store sales up 1.9% in the quarter. The company also reported that e-commerce sales rose 35%, slowing from 41% in the previous quarter. The results come as Walmart and Amazon are locked in an arms race to bring packages faster and faster to customers’ homes.