Walker has moved rapidly into the lead in the Iowa polls, and to a near-tie in the national polls (according to the RCP average). In two respects, though, I think his achievement so far in the race is underrated. First: Walker has also shown an unusual breadth of support, drawing from all elements of the party. Second: In the last cycle, nobody really emerged as the anti-Romney candidate. Walker has, at least at this early stage, become the anti-Bush candidate, and shows signs of being headed for more than that.

That breadth and that rise in the polls, though, mean that everyone else who’s running has an incentive to start taking shots at him. Who goes first?