That being said, it is also quite possible that this is nothing but a smear and without the actual names of people, it is impossible to prove or disprove. (And you are right..it is a New York Times-style anonymous source hit piece. I imagine from the Rats, although the GOP could possibly have done it. However, if the GOP were behind it, the paper would gleefully report that "Republican sources" had pointed them to the "illegal workers," giving the paper a double hit piece.)
Yeah, I really don't know who pulled the sword.
I'm not sure a GOP source would be outed though. Anyone with a regular dialogue with the AP reporter could have planted this "anonymously." Even liberal journalists wouldn't burn a regular source over something that hurts a Republican anyway.
Think of all of the "divided Republicans" stories such a source could help generate.