Mesa, Ariz.

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Primed for a fight, Mitt Romney and Rick Santorum traded fiery accusations about health care, spending earmarks and federal bailouts Wednesday night in the 20th and possibly final debate of the roller-coaster race for the Republican presidential nomination.

Santorum, surging in the race, also took his lumps from the audience, which booed when he said he had voted several years ago for the No Child Left Behind education legislation even though he had opposed it.

"Look, politics is a team sport, folks," he said of the measure backed by Republican President George W. Bush and other GOP lawmakers.

With pivotal primaries in Arizona and Michigan just six days distant — and 10 more contests one week later — Romney and Santorum sparred more aggressively than in past debates, sometimes talking over each other’s answers.

Texas Rep. Ron Paul chimed in from the side, saying with a smile that Santorum was a fake conservative who had voted for programs that he now says he wants to repeal. Former House Speaker Newt Gingrich acted almost as a referee at times.

On foreign affairs, all four Republicans attacked President Barack Obama for his handling of Iran and its attempt to develop a nuclear program, but none of the contenders advocated providing arms to the rebels trying to topple the government of Syrian President Bashar Assad.

The most animated clash of the evening focused on health care in the United States.

Santorum said that Romney had used government money to "fund a federal takeover of health care in Massachusetts," a reference to the state law that was enacted during Romney’s term as governor. The law includes a requirement for individuals to purchase coverage that is similar to the one in Obama’s landmark federal law that Romney and other Republicans have vowed to repeal.

In rebuttal, Romney said Santorum, a former Pennsylvania senator, actually bore responsibility for passage of the health care law that Obama won from a Democratic-controlled Congress in 2010, even though he wasn’t in office at the time. Romney said that in a primary battle in 2004, Santorum had supported then-Sen. Arlen Specter of Pennsylvania, who later switched parties and voted for the law Obama wanted.

"He voted for Obamacare. If you had not supported him, if we had said no to Arlen Specter, we would not have Obamacare," Romney contended.