Recent public polling has been scare, but interested parties agree privately that Dinsdale’s late surge is real. To find evidence that his rivals are taking the new threat seriously, look to the Nebraska airwaves.

The Madison Group — a Tea Party-aligned organization that is backing Sasse — recently launched a 60-second radio ad pegging Dinsdale as a “counterfeit conservative.”

And late last week, the Sasse-supporting Club for Growth upped the ante with a six-figure TV ad campaign against Dinsdale, in which an incredulous-sounding narrator highlights the wealthy political newcomer’s alleged breaches with conservative orthodoxy on issues such as raising the debt limit, pegging him as “really liberal.”

In response, Dinsdale has tapped into the $1 million he recently loaned his own campaign in an effort to push himself over the top.