Roll Call reported today, based on a KMOX story, that Russ Carnahan might have tipped his hand about running in the 1st Congressional District against Lacy Clay. Roll Call says that a Carnahan aide said that he'd be running "in the district he lives in," which would currently mean running against Clay. However, they actually left out a key part of the quote (which was included in the KMOX story); the full quote was: “Umm, I’m not trying to be flippant but he will run in the district he lives in.”
The "I'm not trying to be flippant" is a clue that the aide knew that the question wasn't actually being answered. According to Missouri law, Carnahan could move to a new district and run there, so "running where he lives" doesn't really mean much. And this has been confirmed in quotes from Carnahan's office who said that the quote was misinterpreted. Roll call also cites an anonymous "Missouri Democratic source" as saying that Carnahan has been "sniffing around the 1st District for a long time." I wouldn't be surprised if he's exploring his options, but please keep in mind that both Antonio French and the St. Louis American have pointed out that there are St. Louis political operatives who have a vested interest in pushing for a primary fight.
I suppose it's possible that saying he'd run "where he lives" is a way of testing out some messaging he would use if he decided to run against Clay, but reading too much into a quote from an aide who was clearly instructed not to reveal his decision would be a mistake.