Opinions differ on why Pawlenty fizzled out early, with a popular explanation being the catch-all of “lack of charisma.” It may also be, though, that there was no room in the primaries for a candidate just one notch to the front-runner’s right. Pawlenty couldn’t compete with Mitt Romney for establishment support and couldn’t compete with Michele Bachmann, Herman Cain, and the rest for the hearts of conservatives. Walker may suffer a similar problem. Support for taxing Internet sales is not the type of position that would sink a front-runner, but it is the type of position that could make it harder for a would-be challenger to the front-runner.

If Walker were to become a leading contender, the man he would presumably be trying to beat is Chris Christie. By 2016, Republicans might be as desperate to win the White House as Republicans were in 2000 or Democrats in 1992, and thus be willing to put up with ideological deviations. Christie’s deviations have been numerous enough to win him a reputation as a moderate. Yet neither individually nor in aggregate do they seem likely to be as troublesome in the primaries as those of the last two nominees were. McCain had tangled with conservatives on taxes, global warming, immigration, and many other issues. Romney was out of step with the party on health care, the top domestic-policy issue of the Obama years, and also had a moderate history on abortion, guns, and other issues. Nothing Christie has done seems comparable, and he has a draw those two men lacked, namely his rhetorical combativeness toward liberals. (This is also something that sets him apart from other would-be establishment candidates, such as Ohio governor John Kasich.)