As I've said repeatedly, whatever concerns conservatives may have about Tommy Thompson, he is still a political force of nature in this state. It's also notable that Eric Hovde's considerable spending has garnered him no better than 3rd place. Hovde was spending the money when the state was fixated on the recall election of Governor Scott Walker, he is still largely unknown despite the spending and he entered the race very late. Only time will tell if he can overcome all of that. Further, he and Neumann are vying for the same votes to the right of Thompson.
There are just less than two months left with 26% undecided and it's just one poll, but it continues to be Tommy Thompson's to lose.