The search should perform the latter search automatically and render the article suggestion as first result when available (even if the search is not automatic, it should be much clearer that the first link there is an article and would not continue the search, more like "Wikipedia has an 'article on Barack Obama'", one reason being that that is how it works on Google).
The challenge of this approach is that Google doesn't always do it. They seem to have a sophisticated algorithm behind it that sometimes shows the results of the original query, and sometimes of the "did you mean..." query. In some cases (e.g. when there is no results) it will probably be easy to implement it, in others not so much (given that our current "did you mean..." engine can be wildly inaccurate and thus provide useless first results).
r.