LIVONIA, Mich. — Mitt Romney on Tuesday denounced rival Rick Santorum's automated phone calls urging Democrats to vote against the former Massachusetts governor, calling the tactic "outrageous and disgusting."

"We don't want Democrats deciding who our nominee is going to be," Romney said in an interview on "Fox and Friends."

Santorum's campaign is calling Democrats in Michigan, urging them to vote in Tuesday's GOP primary, which is open to members of other parties. The call urges them to vote against Romney because he opposed the government bailout of the auto industry.

Romney called it a "terrible dirty trick" and "a new low for his campaign."

However, in 1992, Romney took advantage of a similar election rule in Massachusetts.

ABC News reported in 2007:

That year, Romney, then a registered independent, voted for former Sen. Paul Tsongas in the 1992 Democratic presidential primary. He told ABC’s George Stephanopoulos ... that his vote was meant as a tactical maneuver aimed at finding the weakest opponent for incumbent President George H.W. Bush.

"In Massachusetts, if you register as an independent, you can vote in either the Republican or Democratic primary," said Romney, who until he made an unsuccessful run for Senate in 1994 had spent his adult life as a registered independent. "When there was no real contest in the Republican primary, I’d vote in the Democrat primary, vote for the person who I thought would be the weakest opponent for the Republican."

It is difficult to measure the effectiveness of this tactic, which political scientists call "raiding." William Mayer, a professor at Northeastern University, told ABC News that it is believed to be a rare phenomenon.

Both campaigns are waging all-out efforts to bring supporters to the polls because the race between Romney and Santorum in Michigan is neck-and-neck. Romney predicted victory during a rally Monday night, just hours before voting began.

"I'm going to win in Michigan and I'm going to win across the country," Romney told the 1,000 or so supporters who crowded into the Royal Oak Music Theatre on Monday night for his last rally before voting began Tuesday.

The stakes are high for Romney: he was born and raised in Michigan and a loss here would be hugely embarrassing and could deal a strong blow to his campaign.

Romney spent the past five days campaigning hard in Michigan, selling himself as a native son steeped in the auto industry that has defined the state for decades. He has a strong lead in Arizona, which also votes Tuesday.

Appearing Tuesday on Fox News Channel, Romney also said his experience in private business made him the best candidate to deal with the nation's struggling economy.

"Sen. Santorum has shown himself to be an economic lightweight," Romney said. "And I don't think people want to nominate an economic lightweight to go up against the president, who also is an economic lightweight and has it made it hard for America to get working again."

Romney was forced to play catch-up in Michigan after losses to Santorum on Feb. 8 in Minnesota, Missouri and Colorado. While still leading in delegates, Romney fell back in polls. A loss in Michigan would seriously damage the campaign of the on-again, off-again front-runner and probably stretch an already lengthy GOP nominating contest even more.

The Michigan fight has tightened in recent days as Romney's campaign and its wealthy super PAC allies have attacked Santorum in TV ads. Romney has been attacking Santorum's credentials as a conservative, while the former Pennsylvania senator has told voters that Romney can't be trusted to uphold socially conservative principles.

Romney and his allies now turn their attention to the 10 states that vote March 6, Super Tuesday. Romney's campaign bought more TV airtime for ads in Ohio while the super PAC Restore Our Future plans to spend more on TV ads in Ohio, Tennessee, Georgia and Oklahoma.

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