Walmart's biggest threat comes in the form of Amazon and other e-commerce websites, in my view. Amazon and other online retailers continue to gain ground as they move forward with expanding their products and aggressively price their products at comparable or better price points than traditional stores. People are finding it more and more convenient to just shop online, even for groceries nowadays. That's part of the reason why Walmart is testing online ordering with curbside pick-up in select cities around the country now, in an effort to be more convenient to the customer. That's still not as convenient as having your items delivered directly to your front door, like with Amazon, so it remains to be seen whether or not this new, free service has any impact.  Plus too, Walmart faces a less serious but still nonetheless damaging threat of low-price competitors like Aldi and WinCo that cater specifically to those customers that care most about price and do some or all of their shopping at these more affordable stores. These customers don't care about having to bag their own groceries or that there isn't a full service counter like deli. They will either do all their shopping at these stores or do most of it there and shop Walmart, Kroger, etc... "selectively" for only stuff they can't get at Aldi or WinCo.

Kroger better watch out. What is happening to Walmart can and will happen to Kroger.