(An update, with an explanantion of what Corwin does, is here.)New Mexico Gov. Bill Richardson challenged his opponents in February to sign a pledge to run a clean campaign. And he's apparently hired a private investigator to enforce it.

A rival campaign noticed and sent along a line from his second quarter disbursement schedule showing a payment of $12,500 to one Michael Corwin, a PI from Albuquerque.

It's fairly unusual for a campaign to hire a licensed PI for its research team. Judd Legum, Devorah Adler and Christina Reynolds are the research directors of the Clinton, Obama and Edwards campaigns respectively. Difference is: you can't hire them if you want to find out whether a spouse is cheating.

Most opposition research these days is done by lap-top and involves the occasional trip to a courthouse or state records warehouse.