The four GOP presidential candidates had one last chance to state their case in front of the nation before Tuesday's primaries in Arizona and Michigan. Did one candidate stand out from the rest? Here are five things we learned from the CNN Arizona Republican Presidential Debate.

Santorum weighed down by Washington

It wasn't just that Romney and Ron Paul pressed him on his past support for earmarks, the Title X family planning program, the 'No Child Left Behind' education bill and his endorsement of moderate Republican Senator Arlen Specter over conservative Pat Toomey in the 2004 Pennsylania Senate primary.

Santorum made matters worse for himself by aggressively defending his Beltway votes.

He said he was "proud" to stand up for earmarks -- which many conservatives view as wasteful government spending -- after being elected to the House in 1990 and then to the Senate in 1994.

"Congress has a role of allocating resources when they think the administration has it wrong," Santorum said. "I defended that at the time. I'm proud I defended it at the time, because I think they did make mistakes. I do believe there was abuse, and I said we should stop it, and as president I would oppose earmarks."

His reputation probably wasn't helped by the fact that Google searches for the word "earmark" spiked dramatically during the debate, soaring upward by 2300%.

Santorum's explanation of his vote for 'No Child Left Behind' was even more complicating.

"I have to admit, I voted for that," he said. "It was against the principles I believed in, but, you know, when you're part of the team, sometimes you take one for the team, for the leader, and I made a mistake."

His comment drew boos from the crowd, but Santorum pushed forward.

"You know, politics is a team sport, folks," he said. "And sometimes you've got to rally together and do something."

To some conservatives, it may have sounded like Santorum was admitting to being part of the big government problem during the George W. Bush administration.

Santorum's labored defense of his Capitol Hill resume not only reinforced the accusation that he is a tainted Washington insider. It also undermined the central theme of his candidacy, that he is the only true conservative in the Republican race.

Santorum's defiance has its limits

Santorum seems incapable of defending his record without going into extensive and sometimes problematic detail, often with a hint of annoyance. It's not a new phenomenon.

When pressed about his record on the campaign trail, Santorum seems to relish verbal combat and defiantly spars with questioners, as his infamous January back-and-forth over same-sex marriage with college students in New Hampshire demonstrated.

"I'll defend everything I say," Santorum told reporters Wednesday after a rally in Phoenix.

But now that he's in the spotlight as the national Republican frontrunner, Santorum is struggling to stick to the campaign playbook that says a candidate should deliver concise answers and move on.

Santorum's senior adviser John Brabender said his candidate has trouble letting some accusations go unanswered.

"The question is, should he just be fighting back against Romney, or should he be explaining his record," Brabender said. "It is his record, and I think he feels like he has a responsibility to defend it."

Romney was happy to let him do that on Wednesday.

Romney still tacking right

Mitt Romney is no longer playing it safe when it comes to debates, framing his answers carefully with an eye on the general election.

Just over a week after declaring himself "severely conservative" in a major address to party activists in Washington, the former Massachusetts governor made a similar argument in Mesa.

"Severe, strict," Romney said when asked what he meant by his "severely" line. "I was, without question, a conservative governor in my state."