After weathering a media firestorm this past week over a series of provocative comments he made regarding President Obama’s religion, prenatal testing and other issues, former senator Rick Santorum (R-Pa.) had entered Wednesday night’s presidential debate in Mesa, Ariz., aiming to portray himself as the “authentic” candidate and only consistent conservative in the race.

Instead, he fell fall short of that goal.

Santorum, who has been riding a surge of momentum in the polls, found himself struggling to defend his record in Congress as his presidential rivals blasted him on earmarking, contraception and the No Child Left Behind law at the CNN debate, the last showdown before next month’s Super Tuesday contests.

“Politics is a team sport, folks,” a resigned Santorum said at one point when challenged to explain his support for George W. Bush’s signature education law, which Santorum had later said he regretted supporting.

He explained Wednesday night that he’d backed the law because sometimes in politics it’s necessary to “take one for the team” – an explanation that contrasted sharply with his previous scrappy debate performances, and one that’s likely to leave him vulnerable to criticism ahead of key primaries in Arizona and Michigan next week.

Romney, in turn, came under fire for his newly-released tax plan, which Santorum argued amounted to “raising taxes on the top one percent, adopting the Occupy Wall Street rhetoric.” Santorum also questioned Romney’s record as governor, saying he required hospitals to provide the “morning after” pill to victims of rape, a charge that Romney dismissed as untrue.

The debate, sponsored by CNN and held at the Mesa Arts Center, was the 20th of the primary race and is perhaps the final showdown of the GOP primary race. It came as Santorum is eroding Romney’s lead in several key states, including Michigan and Arizona.

Also taking part in the debate were former House speaker Newt Gingrich (R-Ga.) and Rep. Ron Paul (R-Texas), both trailing in the polls. Texas Gov. Rick Perry (R), who dropped his White House bid and endorsed Gingrich last month, was also in the crowd, seated next to Gingrich’s wife, Callista.

Paul, who has begun airing sharp attack ads against Santorum, kept his sights trained on the former Pennsylvania senator Wednesday night, reprising his charge that Santorum is “a fake” and arguing that he has previously supported Planned Parenthood.

Gingrich, meanwhile, took a lower profile than during previous debates, although he made the claim at one point in the night that “not once in the 2008 campaign did anyone in the elite media ask Barack Obama why he voted in favor of infanticide.”

With an eye toward regaining lost ground in the race, Romney on Wednesday released a new tax plan hours after President Obama released his own tax proposal.

In response to Santorum’s criticism, Romney contended Wednesday night that his plan is “going to cut taxes on everybody across the country by twenty percent,” including taxes on the very wealthy.

Romney’s plan includes changes such as lowering the top tax rate from 35 percent to 28 percent and reducing the corporate tax rate to 25 percent. The White House plan, meanwhile, would cut the corporate tax rate to 28 percent and would raise revenue through closing various loopholes and eliminating deductions.

Romney also found himself defending his contention during a speech at the Conservative Political Action Conference earlier this month that he had a “severely conservative” record as governor of Massachusetts.

Asked to clarify what he meant, Romney doubled down: “Severe. Strict. I was without question a conservative governor in my state.”

But it was Santorum who had the most at stake in the debate – and who floundered when challenged time and again by his rivals on various parts of his record as senator from Pennsylvania, such as his record on earmarking.

“What happened is there was abuse,” Santorum said of the legislative pet projects. “When abuse happened, I said we should stop the earmarking process. But I did say there were good earmarks and bad earmarks.”

He then pivoted to offense, attacking Romney for having sought earmarks for the Salt Lake City Olympics in 2002. But Romney appeared to turn back the attack with ease.

“While I was fighting to save the Olympics, you were fighting to save the Bridge to Nowhere,” he told Santorum.

Romney also hammered Santorum for his support in 2010 of Arlen Specter, the longtime Pennsylvania senator who changed parties and ran as a Democrat when faced with a tough primary challenge from conservative former congressman Pat Toomey. The endorsement has haunted Santorum on the campaign trail, and Romney on Wednesday slammed the senator’s explanation of his support as “tortuous.”

A CNN/Time/Opinion Research poll released Tuesday showed Romney taking 36 percent in Arizona to Santorum’s 32 percent, with Gingrich taking 18 percent and Paul garnering six percent. And surveys in Michigan also show the momentum in the race is on Santorum’s side, in large part because former supporters of Gingrich are now flocking to the former Pennsylvania senator’s side.

The Arizona debate was to be followed by another CNN debate early next month in the Super Tuesday state of Georgia. But Romney, Paul and Santorum all signaled that they would not participate, and plans for the debate were scrapped.

Noteworthy about the debate was the fact that all four candidates were seated together at a table, as opposed to standing, as they have done at previous debates; the format meant that they were lobbing heated attacks at one another while seated somewhat uncomfortably side-by-side.

At one point in the debate, the candidates were asked to explain themselves in one word, “without caveats or explanations.”

Ron Paul’s answer: “Consistent.”

Santorum? “Courage.”

Mitt Romney: “Resolute.”

And Newt Gingrich answered, “Cheerful.”