Don’t look now, Amazon. Walmart is coming for your customers

The first sign that something had changed was the Topo Chico. It arrived on our porch one afternoon—a case of it—along with Graza olive oil and La Roche-Posay face wash. When our 4-year-old announced she would eat nothing but Uncrustables for the foreseeable future, a box arrived within the hour. The prices were lower than on Amazon, and we got them faster, with no delivery fee. It turns out that my husband had gotten hooked on Walmart—all without ever setting foot in a store. Earlier...