To be fair in the very same sentence they name several people without full middle names: "Plaintiffs hereby sue Barack Hussein Obama, Eric Holder, Keith B. Alexander, Lowell McAdam, Roger Vinson".

Emphasizing Hussein seems pretty intensional.

EDIT: In fact, looking further: Eric Himpton Holder, Jr. probably isn't legal without the Jr. And Clyde Roger Vinson was missing the entire first name. Lowell C. McAdam and Keith B. Alexander, clearly have middle names, even if I can't find them in a 5 second google search.

Basically they used the common public names for everyone but Obama.

Obama has been subject to some rather curious use of and emphasis on his middle name by his political opponents, largely in connection to implicit or even explicit conspiracy theories that he's secretly a Muslim. If you ever hear someone do it, you'll notice immediately -- the "Barack" and the "Obama" will be quieter and come out very quickly, while the "Hussein" will be spoken loudly, clearly, slowly, and often with emphatic pause before and after, to draw attention to it.

This has the lingering effect of tarnishing the credibility of anyone who uses his full name even for innocent purposes.

For a while during the 2008 campaign it was a bit of a meme to do the same to McCain ("John SIDNEY McCain") and imply that he was secretly Australian, as a way of pointing out how ridiculous the whole thing was.

Somehow I have a feeling jemfinch really didn't know that was his middle name.