The sheriff's office in Richland County, S.C., is investigating a report -- prompted by a photo of the event published in a British tabloid -- that Olympic hero Michael Phelps smoked marijuana there. It's possible Mr. Phelps will be prosecuted. That's right: For those of you who don't know, marijuana is illegal.

I'm guessing it won't take much investigating to discover that Mr. Phelps used the drug at a University of South Carolina house party last November. After all, the 23-year-old swimming phenom -- whose feats in the...