That sound you hear? It’s the fat lady singing.

For the umpteenth time in the Republican presidential primary race, Mitt Romney defeated Rick Santorum in a major Midwestern swing state — a win that effectively forecloses any chance that the former Massachusetts governor might not be the GOP nominee in the fall.

Romney’s victory in Wisconsin was consistent with the polling conducted in the runup to the vote. He was also buoyed by easy victories in the lower-profile primaries held in Maryland and the District of Columbia.

Santorum’s camp claimed earlier Tuesday that the Wisconsin result mattered little to their calculus, insisting that the former Pennsylvania senator would remain in the race at least until his home state votes on April 24.

“If we win Pennsylvania it will give us great momentum going into May, which is setting up to be a big month for us,” said Santorum senior strategist John Brabender.

Santorum, of course, can stay in the race as long as he likes. But, his large delegate deficit coupled with defeats in big — and symbolically important — states like Michigan, Ohio, Illinois and Wisconsin mean the political oxygen is out of the room for Santorum.

While Santorum seems likely to labor on until the Pennsylvania primary, the race was already moving on without him before the Wisconsin vote.

On Monday, President Obama’s reelection campaign launched ads in swing states linking Romney to “Big Oil”. Then in a speech to the American Society of News Editors (ASNE) in Washington on Tuesday, Obama went after Romney for his support of the budget plan put forward by Wisconsin Rep. Paul Ryan (R).

Romney, too, has begun to put the primary fight behind him — worried less about a late sneak attack from his ideological right than the need to begin engaging Obama.

“Maybe it’s time to get going,” Romney said in an interview with conservative talk show host Sean Hannity on Tuesday. “This is time for us to start focusing on [President Obama] rather than standing and focusing on one another in these primary contests.”

And, in his victory speech in Wisconsin tonight, Romney used some of his most pointed language yet when talking about President Obama and his alleged lack of accomplishments over his first four years in office.

“It’s enough to make you think that years of flying around on Air Force One, surrounded by an adoring staff of true believers telling you what a great job you are doing, well, that might be enough to make you a little out of touch,” said Romney.

While Romney and his team have already begun to focus the majority of their time on Obama, the exit polling out of Wisconsin continues to demonstrate that Romney has yet to fully unite the party and will need to find ways to do so — perhaps by picking a conservative vice presidential nominee? — in the coming months.

Among the Wisconsin voters who said that being a true conservative was the most important candidate trait for them, Santorum took 61 percent while Romney won 13 percent.

And, despite being the de facto nominee, Romney beat Santorum by just three points among “very conservative” voters and lost among self described evangelical voters.

Still, Romney’s two-state-plus-the-District sweep amounted to an exclamation point on a race that, in recent weeks, had started to feel like a run-on sentence.

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