"Everyone that follows Amazon is jumping up and down about how exciting this is," Zolidis told Business Insider. "But this was expected." Same-day shipping, not one-day shipping, is the "real battleground" for retailers, and Walmart and Target are well positioned to win that war, he said. In conversations last October with Walmart CEO Doug McMillon, McMillon characterized same-day shipping as the "final frontier" that "everyone is racing to develop," Zolidis said. Walmart did not immediately respond to a request for comment on this story.