Mitt Romney’s win in the Wisconsin primary on Tuesday night effectively sealed the Republican presidential nomination for the former Massachusetts governor.

While most people are content to look at the topline numbers — Romney beat former Pennsylvania senator Rick Santorum by five points — the Fix likes to get our hands really dirty by digging into the exit polling in search of how Romney won.

That’s what we spent the morning after doing. Our five key takeaways from the Wisconsin exit poll are below.

1. Romney’s margin was held down by Democrats.

Among self identified Republicans, who comprised roughly six in ten of all voters in Wisconsin, Romney beat Santorum by a convincing 50 percent to 37 margin. But among the 11 percent of the electorate who identified themselves as Democrats, Santorum won 44 percent to 23 percent. Given that Santorum’s issue stances are anathema to Democrats, it’s hard to imagine Santorum’s margin among them as anything but a bit of mischief-making by the rival party — hoping to keep the GOP primary fight going on a little longer.

2. Romney won on electability....

As has been the case throughout this primary process, Romney’s victory in Wisconsin was built on the fact that a plurality of voters see an ability to beat President Obama as the key trait when picking a candidate. Of the 37 percent who cited electability as the most important attribute in their vote, Romney crushed Santorum 67 percent to 23 percent.

3. ...And on inevitability.

Human nature dictates that we like to be with the person who looks like the winner. (Hence the term “bandwagon fan”. Or, L.A. Lakers fan.) And in Wisconsin, it became clear that voters had decided that Romney was going to be the GOP standard-bearer. Eighty percent (!) said that Romney was the likely presidential nominee while just 12 percent named Santorum. Among the eight in 10 who said Romney would be the nominee, the former Massachusetts governor won by 20 points over Santorum.

4. Romney won over the tea party. Sort of.

The former governor’s moderate tone on issues — he doesn’t call President Obama a “socialist”, for one — ensured that he would never be the candidate for and of the tea party. But Romney has ground down opposition among strong tea party supporters with a relentless focus on how Obama has failed on the economy and how he would do better. Among “strong” tea party supporters, Romney beat Santorum by 12 points in Wisconsin — evidence of the progress he has made. Of course, just 32 percent of primary voters in Wisconsin said they were strongly supportive of the tea party. Romney has won only two states — Nevada and Florida — where more than one in three voters in a primary or caucus called themselves strong tea party supporters.

5. Endorsements don’t matter.

Only one in four Wisconsin voters said Romney’s series of endorsements — Wisconsin Rep. Paul Ryan and Wisconsin Sen. Ron Johnson, among many others, endorsed Romney in recent days — were one of several important factors in deciding their vote. (Among that group Romney, not surprisingly, beat Santorum by more than 40 points.) Two-thirds of Wisconsin voters said the endorsements were either a minor factor or no factor at all. While those numbers might be artificially low — people tend not to like to admit their minds were made up by what some politician told them to do — they do serve as a reminder that while endorsement are nice, they aren’t decisive.

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