Otus News/ ABC News / By MATTHEW NEGRIN

The first words out of Mitt Romney's mouth at tonight's Republican debate were a planned attack on Rick Santorum.

Time and time again on stage, Romney turned to his right to label Santorum a spender of government money who favored earmarks, not the conservative he has proclaimed himself throughout his campaign.

Romney's premeditated talking-point barrage reflected the stakes of the GOP primary. Once considered the inevitable nominee, Romney is facing the prospect of a troubled campaign should he lose a primary Tuesday in either Michigan or Arizona.

At one point during the debate that aired on CNN, Romney sought to use one of his biggest albatrosses with conservatives, his record on health care, against Santorum by accusing the resurgent candidate of being responsible for "ObamaCare" by endorsing a candidate who became a Democrat, Arlen Specter.

"So don't look at me," said Romney, whose health record in Massachusetts has been called a model for the federal program signed by President Obama. "Take a look in the mirror."

Santorum's defense was that he backed Specter because the Republican-turned-Democrat vowed to support President Bush's judicial nominees.

Romney and Santorum also volleyed insults during a tense exchange over earmarks.

It began as Santorum argued that while he was a senator he supported "good earmarks," such as essential military weapons, but that not all spending projects are appropriate. However, he said, "as president, I would oppose earmarks."

"I didn't follow all of that," Romney countered.

He then defended his role as the head of the Olympics, in which he asked the federal government for money to cover transportation and security costs.

Romney conceded that he agreed with Santorum over giving the president line-item veto powers, but he insisted that they differed on their approaches to government spending.

"While I was fighting to save the Olympics, you were fighting to save the bridge to nowhere," Romney jabbed, referring to the infamous earmark that came to symbolize wasteful spending.

Ticking off some highlights from Santorum's record as a senator, Romney told the crowd in Arizona that the Pennsylvanian raised the debt ceiling "five different times" without insisting on cuts in spending to balance it, funded Planned Parenthood and voted to expand the Education Department.

"Senator, during your term in Congress, the years you've been there, government has doubled in size," Romney said. "In my view, we should not raise the debt ceiling again until we get compensating cuts in spending."

Santorum, sitting in the spotlight on the stage as the nominal frontrunner, fought back by accusing Romney of saying he would also vote to raise the debt ceiling.

However, Santorum added, he regretted some of his votes, including one in favor of the much-maligned No Child Left Behind education bill.

He also accused Romney of wanting to raise taxes - at least on the top 1 percent of Americans.

"I'm not going to adopt that rhetoric," Santorum said. "I'm going to represent 100 percent of Americans. We're not raising taxes on anybody."

Though the debate also featured a handful of questions about social issues, the candidates were more in agreement as they derided the Obama administration for what they said were attacks on religion, and they called for cultural matters to be addressed.