NEW YORK (

TheStreet

) -- Rick Santorum decided in his newest advertisement to attack Mitt Romney's negative campaign tactics as the former Pennsylvania senator's rapid climb in national and state GOP primary polls has fueled his confidence.

The ad called "Rombo" shows a Romney look-alike prowl through an empty building as he shoots mud at cardboard cutouts of Santorum.

Rick Santorum

"Mitt Romney's negative attack machine is back on full throttle. ... Romney and his super PAC have spent a staggering $20 million brutally attacking fellow Republicans," the ad's narrator says.

Splotches of mud zing past the Santorum cutout as patriotic music plays in the background. After every volley misses, Romney runs out of ammunition and mud suddenly bursts on his white shirt.

"And in the end, Mitt Romney's ugly attacks are going to backfire," the narrator says.

Santorum has mostly avoided negative attacks as his campaign has run on a shoestring budget, but with a lead of nine percentage points in Michigan -- Romney's home state -- it appears the candidate will make a serious play for a state that a week ago seemed unattainable.

-- Written by Joe Deaux in New York.

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