1. While Tommy may have highrollers on speed dial, his Wisconsin contacts are still on a Rolladex.
As Governor, he put in long hours appearing in every corner of the State, and was very accessible. One to one, if you were having a problem with the State bureaucracy, and the request was reasonable, he'd try and help out.
His problem, now, many of those folks he helped out are now deceased, or moved to Florida.
He managed the long hours for a few weeks in Iowa for his abortive Presidential run, but it was wearing him out. I don't think he can sustain it all the way to November, and Russ doesn't give much to work with on a strictly negative ad-driven campaign. Unlike his opponents in the Governor races, they won't beable to paint Feingold as a gungrabbing nannystater. (Feingold voted against renewal of the assault weapons ban, a position that synchs well with his battle against the PATRIOT ACT.)
2. I don't think Tommy's heart will be in it. He's been enjoying time with his grandkids, and hated living in Washington, hence the long delay in making up his mind. In agreeing to go through the motions, I suspect it's just to neutralize, as best he can, Russ' coattails in the races for the Legislature.
3. The first debate.
4. The Tea Party crowd. if he goes into full pander mode, he blows off those who consider him legitimately a "compassionate Conservative." if he doesn't pander, they've time to field an Indy/3d party guy. it's telling that Tommy skipped the tea party convention in the Dells, where he might well have been booed over his pre-flip position on Healthcare reform.