It isn't all due to Romney's choice of Wisconsinite Paul Ryan as his running mate. The Badger state has been trending GOP in recent elections thanks to a plethora of good candidates and excellent organizations. Not only has Wisconsin elected a Republican senator and governor since 2010, but the legislature went GOP for the first time in 12 years.

But the Ryan pick may have crystalized support for Romney in the state:

CNN:

CNN Thursday turned the important battleground state of Wisconsin from "lean Obama" to true "toss up" on its electoral map, in the wake of Mitt Romney's naming of House Budget Chairman Paul Ryan, a seven term congressman from the Badger state, as his running mate.

One contributing factor behind CNN's move was a new poll that matched two others from last week that indicate that the presidential contest in Wisconsin is close. While Ryan's announcement did not dramatically alter the presidential poll numbers in Wisconsin, it did change the way both campaigns viewed the state of the race in the state.

"Both campaigns see the Ryan pick as something that makes Wisconsin more competitive. When we visited this week, every Republican we spoke to suggested it would help keep a Republican base already energized by the recent recall election fired up and hungry for more in November." said CNN Chief National Correspondent John King.

"And we saw the impact on the Obama campaign firsthand. Within hours they rewrote their script for calls to voters to add some sharp criticism of Ryan and his Medicare plan. But the way they did it was telling: A couple of lines about how is a nice guy, sure, but then the segue to the attack and a script that included a line saying President Obama was more in tune with working class voters," added King.

According to the CNN/ORC International survey, which was conducted entirely after Romney added Ryan to the GOP ticket, 49% of registered voters in Wisconsin say they back President Barack Obama, with 45% supporting Romney. The president's four point advantage over the presumptive Republican presidential nominee is within the survey's sampling error.

The last GOP candidate to take Wisconsin was Ronald Reagan in 1984. Since then, Republicans have come very close but failed to break through. In 2008 Obama won by 14% so it's been a long way back for the GOP. A four point spread in a poll that oversamples Democrats probably means that the race in that state is tied. And even if Romney doesn't win, he is forcing Obama to devote resources and precious time campaigning to hold on to the state.

A win-win scenario for Romney in any case.