Remember Herman Caine? Rick Santorum? Newt Gingrich? All of them were strong out of the gates and then the Romney team (a.k.a. GOP establishment) trained their sites on them and laid down a constant barrage until they were shattered. There is nothing the GOP-e hates more than conservatives, certainly they hate them more than democrats and liberals. If Walker continues to rise he will take on heat like the underside of the space shuttle re-entering the atmosphere.
Interestingly though, Walker has been getting hammered for years by unions and dem apparatchiks for years now and he's shrugged it all off and just kept winning. So it will be interesting to see how he stands up when his "friends" try to stick a knife between his ribs.