What Part Of "Citizen" Don't They Understand

From the AP's coverage of the last Democratic debate in Iowa comes this gem:

The discussion of immigration was in sharp contrast to the Republican debate last week in which the GOP candidates tried to outmaneuver each other on who would be tougher on illegal immigrants. The Democratic candidates said they were not willing to encourage Americans to arrest illegal citizens.

Huh?

What the heck does THAT mean? "Illegal citizens?" I can honestly say that phrase means absolutely nothing. Do they mean "Americans citizens engaged in illegal activity" or "people who have obtainted citizenship through some fraudulent or other illegal means?"

Is the AP trying to say--or rather, trying NOT to say--"illegal immigrant?" Why is it so hard to just use the accurate, indisputable, opinion-neutral phrase?

In their efforts to avoid giving offense to immigration crimina...er "uninvited entrants," the AP is giving far more offense to users of the English language.