Last month we reported that the District’s first official triathlon, the Nation’s Triathlon, was a go. After months of haggling with competing jurisdictions for permit, race organizers got the final go-ahead for the event, which would include a swim in the Potomac River, a bike ride up Rock Creek Park, and a run to the U.S. Capitol and back. Plenty of readers made jokes about swimming in the Potomac. Hell, so did I –…