From a consumer perspective, K-Mart was failing before everyone started rushing to China. And Walmart's US logistics was way ahead of everyone else, which is what enabled them to have lower prices. Target succeeds due to having products that actually look good, as opposed to Walmart, whose style is distinctly lack-of-style. I remember going to K-Mart, and Walmart easily beat them without needing to go to China.
I'm not sure I see what kind of supply chains Walmart has in China, since it mostly sells other companies' goods. Maybe it produces the house brand (can't remember the name) in China itself, but I wouldn't be surprised if it outsources that.