Early in the cycle, the Missouri Senate race appeared to be one of the toughest fights of 2010. But as one interesting Senate race after another cropped up on the map — Florida, Wisconsin, Washington, Nevada, Pennsylvania, Arkansas — the race between Roy Blunt and Robin Carnahan has slipped down the list, and is easy to overlook.

Polling has been pretty sparse and dominated by Rasmussen; Blunt has led every poll conducted since January by one to eight percentage points.

What probably ought to worry Democrats is that their allies have been hammering Blunt with tons of negative ads — $1.3 million worth from the League of Conservation Voters, ProVote, and Vote Vets — with not too much to show for it. At the end of March, PPP found 34 percent having no opinion about Roy Blunt. One might think those negative ads could define him early, but it appears they haven’t yet.

And these Carnahan-allied groups no longer have the airwaves to themselves. Blunt’s campaign is airing its first ad, airing statewide: