With the latest polls showing a dead heat in Michigan, the leading Republican presidential candidates are taking swipes at each other just hours before voters will head to the polls.

The latest spat between former Pennsylvania Sen. Rick Santorum and former Massachusetts Gov. Mitt Romney is over a Santorum "robocall" campaign that targets Democratic voters.

CBS News reportsthat the automated calls to Michigan voters highlight Romney's opposition to the auto industry bailout of 2008 and 2009.

"Michigan Democrats can vote in the Republican primary on Tuesday," the voice on the call says, according to CBS. "Why is it so important? Romney supported the bailouts for his Wall Street, billionaire buddies, but opposed the auto bailouts. That was a slap in the face to every Michigan worker, and we're not going to let Romney get away with it."

The call asks Michigan Democrats to "send a loud message" to Romney by voting for Santorum and it ends with this: "This call is supported by hard-working Democratic men and women and paid for by Rick Santorum for president."

Santorum, by the way, also opposed the auto bailout and he previewed this line of attack during last week's debate in Arizona. Santorum said he opposed both the auto bailout and the financial bailout on principle, while Romney opposed the auto bailout, but supported one for his friends on Wall Street.

Politico reports that Romney came out swinging on Fox News this morning.

"It's a dirty trick," Romney said about the robocalls on Fox & Friends. "It's outrageous to see Rick Santorum team up with the Obama people and go out after the union labor in Detroit to try to get them to vote against me. Look, we don't want Democrats deciding who our nominee's going to be, we want Republicans deciding who our nominees are going to be.

"I just think it's outrageous and disgusting, a terrible dirty trick at the last hour, by the way, late in the afternoon on the day before the election, maybe hoping no one would notice, they start sending out calls to Democrats, union members, telling them to go into the Republican primary and vote against Mitt Romney," he said.

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