The real lesson of "Etch-a-Sketch": Romney's rivals haven't made much of his flip-flops

This is not an exhaustive list of Mr. Romney’s policy shifts; the point is simply that his rival campaigns have a lot of ammunition to work with. And yet, they have rarely been able to make much of it.

Tim Pawlenty famously flubbed a line about Mr. Romney’s health care bill during an early debate. Newt Gingrich and his “super PAC” attacked Mr. Romney on his tenure at Bain Capital, but was much more reluctant to go after Mr. Romney’s inconsistencies — possibly because Mr. Gingrich has some apostasies of his own.

Ron Paul, who has perhaps the most consistent voting record of any presidential candidate in memory, has rarely gone after Mr. Romney directly. Jon M. Huntsman Jr. was more willing to, but he was a minor player during most of the campaign, and he lacked the budget to give the slick commercials he had produced on Mr. Romney’s shifts a wide airing on television.

Two rivals, Rick Santorum and Rick Perry, were potentially in a stronger position to attack Mr. Romney on these grounds. But Mr. Romney’s campaign successfully executed the same bold strategy against them, shifting the conversation to highlight their own departures from conservatism. The sequence during the Feb. 22 debate in Arizona, in which Mr. Santorum was initially making an effective attack against Mr. Romney’s health care bill but Mr. Romney turned the conversation around to Mr. Santorum’s endorsement of Arlen Specter, was the clinching moment for that strategy and may have helped Mr. Romney to win Michigan when it voted a week later.