(Image Credit: Dennis M. Rivera Pichardo/AP Photo)

ABC News' Michael Falcone and Arlette Saenz report:

GREEN BAY, Wisc. - Despite the fact that the Republican establishment is rallying around Mitt Romney - or perhaps because  of it - Rick Santorum is closing out his Wisconsin primary battle with a ferocious new television ad that portrays Romney and President Obama as the same person.

At the beginning of the 30-second spot, a narrator walks on to the screen pointing at a photo of Obama: "What if I told you this man's big government mandating health care included $50 abortions and killed thousands of jobs, would you ever vote for him? What if I told you he supported radical environmental job-killing cap and trade and the Wall Street bailouts? And what if I told you he dramatically raised taxes and stuck taxpayers with a $1 billion shortfall?"

"One more thing, what if I told you the man I'm talking about isn't him," the narrator says as a photo of a grimacing President Obama flashes on the screen and then dissolves into a photo of Romney. "It's him."

According to a campaign official, the ad began airing on Monday - the eve of the Badger State primary, which polls show Santorum could lose. And Santorum has shown no signs of easing up on Romney on the campaign trail either.

At an event at the National Railroad Museum in Green Bay Sunday night, Santorum called health care "the most central and important issue in this race." He said that because Romney supported a health care reform plan so similar to the one President Obama backed, Romney is "uniquely disqualified" to be Republican Party's presidential nominee.

"He advocated for the very things that Barack Obama has done. Why? Because he did them  as governor of Massachusetts," Santorum said. "He's uniquely disqualified  and we all know it . All the establishment knows it. It's Barack Obama's Achilles heel and yet we're taking the spear out of our hands."

In response to the new ad and the latest attacks, Romney spokeswoman Andrea Saul said of Santorum: "It is sad to see him completely lose his bearings and revert to patently false claims. Senator Santorum is at a point of desperation that he will say or do anything."