Near enough, the Observer is an extremely left wing rag.
In an age of digital media and free lance writers, the platform upon which an article appears is much less important than the content therein.
For instance you can read Bernie Quigley articles on Conservatives for Palin which no rational conservative would consider left wing.
Furthermore, the notion that the United States should stop subsidizing NATO and leave continental European security to the continental Europeans is well within the wheelhouse of traditional conservative thinking...despite what a few global interventionist trolls here might say.