Seriously fringe conservatives are still challenging Obama's citizenship in court. This fringe group has been given the name "birthers", since the basis of their challenge is that Obama was not born a U.S. citizen, and therefore his presidency is unconstitutional.
Birthers, who had lost previously in courts as well as public opinion, had pinned their final hopes on a federal case in D.C., Hollister vs. Soetoro, et al..
Not only did the judge throw the case out, but he did so in rather harsh language. And he has cited the attorney who brought this suit on frivilous grounds.