Scott Walker's signature Monday on legislation imposing new restrictions on labor organizing made Wisconsin the nation's 25th "right-to-work" state. But more significantly, it marked Walker's return to the union-busting politics that have defined his tenure as a blue-state governor and helped push him into the top tier of Republican presidential contenders.

In working the circuit of early primary cattle calls, Walker's pitch to GOP voters is relatively straightforward: He's a "fresh new face" (in contrast to, say, Jeb Bush), and he's actually succeeded in enacting conservative policies in a state that hasn't voted Republican for president since 1984. As Walker likes to remind audiences, he has also beat back aggressive Democratic challenges three times in a span of four years, including a 2012 recall election that served as a referendum on his push to enact legislation limiting collective bargaining for state employees. "We did it without compromising," Walker boasted at the Conservative Political Action Conference last month. "We stood up and said what we were going to do. And we did."

If you're a conservative primary voter, it's an appealing message, especially when compared to the comparatively paltry record of the Republican Congress in getting results in Washington. Yet Walker's ongoing battle with unions could risk becoming a defining issue for him, and not necessarily in a positive way. This was most clearly illustrated when the one-term governor, obviously not well-steeped in foreign policy, used the 2011 law as an awkward punchline to suggest his victory over Democrats and organized labor qualified him to take on ISIS as commander in chief. "If I can take on 100,000 protesters, " he said at CPAC, "I can do the same across the world.” The clumsy boasting demonstrated his weakness in foreign affairs, but it also came close to exposing him as a one-issue pony. (For an example of how this can become damaging in a presidential race, see: Giuliani, Rudolph W.)

The right-to-work issue was not a major focus of Walker's reelection campaign in Wisconsin. Because of that, Walker's signing of the bill forbidding organized labor from forcing workers to pay into a union was not as predictable as his record might have made it seem. As the Milwaukee Journal-Sentinel noted on Monday, Walker said during the fight over his 2011 anti-labor law that he "wouldn't let legislation affecting private sector unions reach his desk." And as recently as December—after his reelection to a second term—the governor called the right-to-work bill "a distraction" and predicted legislature would be too busy with other issues to bring it up. Those comments caused consternation among conservatives, even drawing a mild rebuke from the editorial board of the Wall Street Journal. But despite his initial efforts to distance himself from the bill, Walker ignored Democrats who urged him to threaten to veto the legislation. With his White House bid gaining momentum, there was little doubt he would sign the bill once the legislation put it on his desk last week.

It's neither shocking nor particularly galling that Walker would tack right on an issue central to his record as governor after glossing over it during his reelection campaign. Voters have seen far more outrageous flip-flops by politicians pursuing the presidency in recent years, and there's never been any question about where Walker stands on unions. (Walker's reported switch on the wisdom of an ethanol mandate may be more obvious pandering.) Thanks in part to the Republican state legislature, the timing of the right-to-work law is most helpful: The bill-signing allows Walker to ditch a topic—foreign policy—that's clearly still uncomfortable for him, in favor of the subject that won him national fame in the first place. Primary voters probably won't care that the right-to-work law wasn't Walker's idea; to them, it's just another conservative win for a governor who revels in battling with the left.