Let this be a lesson: When you think you've identified the one issue on which Mitt Romney has been consistent, think again.
Romney's opposition to unions has been consistent throughout this Republican presidential primary campaign, which is a whole lot of consistency by his standards—one time he said "Unions have played a very important role historically," but that was just in the process of making a slightly more nuanced anti-union argument than he usually employs—but of course, of course it turns out that he was singing a different tune while running for governor in Massachusetts in 2002.
Here's a guy who made his hundreds of millions by laying workers off, cutting their pensions, shipping their jobs overseas—all things unions pretty much exist to combat—and to get his foot in the electoral door he was willing to claim he wanted "cooperation" and was opposed to "partisan posturing" when it came to unions? There goes the one principle I really thought he was firm on.