Rick Santorum found that his position at the top of polls made him the biggest target in Wednesday's CNN Republican presidential debate, possibly the last of the GOP primary and caucus campaign.

Mitt Romney, who has been front-runner off and on through the campaign but saw his momentum blunted by Santorum's recent surge, went after the former Pennsylvania senator over his record in Congress, trying to shoulder past him before Tuesday's primaries in Arizona and Michigan, which most polls show neck-and-neck between the two.

"Voting for the debt ceiling five different times without voting for compensating cuts," said Romney, describing Santorum as a big spender in Congress. "Voting to fund Planned Parenthood, voting to expand the Department of Education. During his term in the Senate spending grew by some 80% of the federal government."

Santorum, who surged to the top of state and national polling after sweeping the February 7 contests in Colorado, Minnesota and Missouri, was sitting center stage next to Romney and was quick to fire back.

"When you look at my record of never having raised taxes -- Gov. Romney raised several hundred million dollars in taxes and fees in Massachusetts. I never voted to raise taxes," Santorum said. "Gov. Romney even today suggested raising taxes on the top 1%, adopting the Occupy Wall Street rhetoric. I'm not going to adopt that rhetoric."

Santorum's opponents joined together to attack a vote he made in support of larger bill that, in part, provided funds to Planned Parenthood.

"If you voted for Planned Parenthood, like the senator has, you voted for birth control pills," Paul charged. "And you literally, because funds are fungible, you literally vote for abortions because Planned Parenthood gets the money ... they have the money left over to do abortion."

Romney followed up aggressively, saying Santorum had not backed away from the vote in a subsequent interview.

Santorum insisted he had always been clear that as president he would defund Planned Parenthood.

"I admit I voted for large appropriation bills and there were things in there I didn't like," he said, but explained he had also created a program that funded abstinence-based education in schools

The candidates confronted each other in a lengthy and contentious argument over the congressional process of earmarking, often derided as "pork-barrel" spending.

"Congress has a role to play when it comes to appropriating money," Santorum declared in a full-throated, detailed defense of the process -- one he said Romney had taken advantage of when he requested funds for the 2002 Olympic Games in Utah.

"I didn't follow all of that," Romney cracked after Santorum finished speaking. While criticizing Santorum for some of the earmarks he supported, Romney defended his request for Olympic funds.

"While I was fighting to save the Olympics, you were fighting to save the 'Bridge to Nowhere,' " he said.

Santorum did not back down, telling Romney: "You don't know what you're talking about."

The former senator said Romney's defense of that Olympic funding request amounted to approval of the earmarking process.

"What you just suggested as to how earmarks should work in the future is exactly how they worked in the past," Santorum said. "So I suspect you would have supported earmarks if you were in the United States Senate."

Romney also came up with a new line of defense against Santorum's repeated attacks on the health care plan passed in Massachusetts when he was governor as being the blueprint for Obama's national health care law by attacking Santorum's support of former Republican Sen. Arlen Specter against conservative challenger Pat Toomey. Specter later switched parties and voted for Obama's health care law.

"If we had said 'no' to Arlen Specter, we would not have ObamaCare," Romney told Santorum.

The two were seated next to each other at a table, flanked by Texas Rep. Ron Paul and former House Speaker Newt Gingrich and often turned to each other as they attacked.

While listening to Santorum's criticism, Romney shook his head or looked slightly to the side with a pained expression on his face. Santorum raised his eyebrows at Romney's attacks at him and looked off to the side as if he was running Romney's words through his mind.

Meanwhile, at several points Gingrich was captured chuckling at the other candidates' statements.

The debate, hosted by CNN and the Republican Party of Arizona at the Mesa Arts Center, was the 20th in the campaign and the last before the candidates will share a stage before primaries in Arizona and Michigan on Tuesday, before Washington state holds a contest on March 3, and before 10 more states hold primaries or caucuses on Super Tuesday on March 6. And no more debates are scheduled. CNN canceled a debate in advance of Super Tuesday after Romney, Santorum and Paul pulled out.

The four last met on January 26 before the Florida primary. Romney went on to win big there and in Nevada, while Gingrich, who had just scored an impressive victory in South Carolina, faded fast.

While Romney and Santorum grew heated at times, Paul deflated the tension a bit when asked why he had labeled Santorum a fake in a television ad that attacked the former senator's conservative credentials.