National Journal's Beth Reinhard suggests that
Wisconsin's political focus on labor is pushing Mitt Romney in a direction he might not otherwise want to go:
In a stark example of the perils of a protracted primary campaign, dangers lurk for Romney no matter what approach he takes in Wisconsin. Tone down the rhetoric he used in Michigan, where he condemned “labor stooges,” and he risks ceding the state to Santorum and further alienating the conservative base of his party. Ramp up the labor-bashing and cozy up to Walker, and Romney risks laying the groundwork for a general-election disaster. [...]
Praising Walker’s efforts follows Romney’s strategy of elevating short-term security over long-term risk. Indeed, in Michigan, he tilted so far in that direction that it raised questions about whether he intended to contest the state in November.
Romney has campaigned against unions so enthusiastically that it may go beyond pure short-term considerations, but we are talking about Mitt Romney here. However enthusiastically he's attacked all things union-related, if he thinks it will benefit him in the general, he'll swing back. That being the case, this is certainly one reason it's great that the Republican presidential primaries are dragging on, even if Mitt Romney ends up the nominee as was generally assumed from the get-go. Michigan and Wisconsin have both voted for Democrats for president over the last several cycles, but both were close in 2000 and 2004; Ohio, where Romney also waged an anti-union campaign, is famously a key swing state. But though he needs to contest those states in the general, at least through the Wisconsin primary, Romney will keep ranting about "union bosses" and the like, making it ever-easier for unions to persuade even Republican-leaning members that a vote for Romney is a vote against their economic well-being.
The longer it takes him to defeat Santorum, the longer he has to wait to shake the Etch-A-Sketch, and the more likely voters are to remember what the Etch-A-Sketch said through the long months of the primaries.