Calling Walmart's Express stores a failure is a bit strong (perhaps completely inaccurate) and comparisons to Target's still-sparse small-format effort are off as well. Unlike Target, Walmart operates a highly-productive mid-sized format (Neighborhood Market) that can take up the slack in smaller markets and these stores more easily wick off of Walmart's existing supply chain processes. Walmart's shuttering of its Express stores should be seen as a testament to the success of its Neighborhood Market format rather than a stand-alone failure.
The more comprehensive (yet navigable) assortments in Walmart's Neighborhood Market stores also further distance it from the legion of true small-format competitors including dollar stores, convenience stores, drug retailers, hard discounters and others.
Target on the other hand is operating in two arenas that are crammed with experienced operators (big box/small box). Not an easy road ahead!