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The Republican presidential candidates head back on the campaign trail Thursday after a debate in Phoenix, Ariz. that, while fiery at times, ultimately changed little in the race for the 2012 presidential nomination.

The debate, which took place one week before a flurry of voting begins with contests in Michigan and Arizona, saw Mitt Romney reaffirm his genteel but biting attack style. His main target was Rick Santorum, who faced a host of questions from his rival aimed at cutting short the would-be path of an emerging frontrunner.

Romney went on offense from the start against Santorum's record of spending while in the U.S. Senate, accusing him of raising the debt ceiling five times, funding Planned Parenthood and expanding the Department of Education.

In a searing first shot the Republican presidential primary frontrunner said during Santorum's watch, spending grew 80 percent of the federal government.

But in a quick retort, Santorum, seated next to Romney one week before they and candidates Newt Gingrich and Ron Paul hear from voters in Arizona and Michigan, said that while he was in office in Washington, the debt as a percentage of GDP went down from 68 percent to 64 percent.

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Santorum added that if he were president, he would cut the budget by $5 trillion over five years but it wouldn't come from defense spending, but from means-testing entitlement programs..

"When I was born, less than 10 percent of the federal budget was entitlement spending. It's now 60 percent of the budget," Santorum said. "Some people have suggested that defense spending is the problem. When I was born, defense spending was 60 percent of the budget. It's now 17 percent. If you think defense spending is the problem, then you need a remedial math class to go back to."

Santorum is in a heated contest against Romney in what has essentially turned into a two-man contest for the nomination to challenge President Obama, surging in recent polls both nationally and in key primary states.

But Romney, who has a wide lead in Arizona, is claiming he's got something none of his opponents has -- a business background. Romney said if he were president, he would go through every single federal program and ask if it is affordable or whether it's worth borrowing money to pay for it.

"And if not, I'm going to get rid of it," he said. "I'm going to take programs that are important, but that could be better run at the state level and send them back to the states as a block grant ... And then ... with what's left of government, I'm going to cut the employment by 10 percent. And I'm going to link the pay of government workers with the pay in the private sector."

Romney said as president he would also veto earmarks, ignoring that the Supreme Court has ruled that the line-item veto is unconstitutional. He also defended his request for earmarks when he went to Congress in 2002 to seek assistance for the indebted Salt Lake City Winter Olympics.

Santorum, who voted for the Olympics earmark, said he was happy to do it because it was a good earmark, but since then he's seen congressional members run away with the privilege.

Gingrich said that earmarks have their place, especially when the president is of the opposite party.

"If you have Barack Obama as president and you have a Republican House, you may want the House imposing things on the president," Gingrich said.

Accusing Obama of kowtowing to the unions, the candidates did agree that the bailout of General Motors and Chrysler was the wrong way to go for the U.S. government and a managed bankruptcy would have been better for the economy

Obama committed an "unprecedented violation of U.S. bankruptcy laws" to pay off the United Auto Workers, Gingrich said, adding, "The fact is Chrysler is now Fiat."

"The government is supposed to protect contracts, they're not supposed to regulate contracts and they're not supposed to undermine contracts," added Paul.

Paul also was quick with his own criticisms of his rivals. Asked why he had a new television ad that labels Santorum a fake, Paul replied, "Because he's a fake."

When Santorum said he had been rated the most conservative of 50 senators in his class, Paul, a longtime Texas congressman, responded: "That's always a cop-out when you compare yourself to the other members of Congress. The American people are sick and tired of the members of Congress. They get about a 9 percent rating."

While the candidates have tried to stay on point with economic issues that they think will be the appropriate lever to sink Obama, the rise of the socially conservative Santorum has coincided with the Obama administration's decision late last month to require religious institutions to pay for insurance that includes contraceptive methods opposed by the Catholic Church.

After heavy criticism, Obama shifted the burden to the insurance companies to pay for the coverage, but many religious organizations said they self-insure and no exception is made for that.

Republicans have said the issue is one of the federal government denying religious groups the practice of their beliefs, but Democrats have argued that Republicans merely want to deny birth control to women.

Santorum, who has spoken on the campaign trail about the impact of government programs that result in more unwed parents, has been particularly targeted for that criticism, something Santorum said he's happy to take on.

"You know, here's the difference between me and the left, and they don't get this. Just because I'm talking about it doesn't mean I want a government program to fix it. That's what they do, that's not what we do," he said.

"If we're going to have a debate about who the extremist is on these issues, it is President Obama who, as a state senator, voted to protect doctors who killed babies who survived the abortion," Gingrich added.

As the remaining GOP candidates conducted their 20th debate Wednesday night, possibly the last in the season, the four have their sites set not only on next Tuesday's contests, but the 10-state Super Tuesday contest on March 6.