The last time we were here - less than an hour before a Republican debate - former Massachusetts Gov. Mitt Romney seemed like the inevitable Republican nominee for president.

Since, we've seen former Speaker Newt Gingrich fade in the polls and former Pennsylvania Sen. Rick Santorum surge. Also since the last debate, Santorum had that Feb. 7 sweep, winning Missouri, Minnesota and Colorado.

Needless to say, the roller coaster of a ride that this Republican primary has been is at a pivotal point. Republicans head to the polls in Arizona and in Michigan, Romney's home state, on Feb. 28 and the polls have so far given Romney the edge in Arizona but predicted a toss up between Romney and Santorum in Michigan. At stake are 59 delegates.

So those two candidates are bound to throw hard punches tonight. As for Gingrich, he has been struggling to raise money so this could be his chance to wedge himself back into the race.

We'll live blog the debate, which is scheduled to start at 8 p.m. ET at the Mesa Arts Center in Mesa, Arizona. We'll also continue using our ALERT system, in which we'll point out "A Line Everybody [will] Remember Tomorrow." In other words, talkers. Make sure to refresh this page often to see the latest updates.

Update at 9:43 p.m. ET. 'Kids First, Unions Behind':

Romney defends No Child Left Behind, saying there are things that should be changed, but that the law has the principles right.

"We have to put kids first and the unions behind," Romney said.

Update at 9:41 p.m. ET. Politics Is A Team Sport:

Santorum receives another set of boos from the crowd, when he said he "took one for the team" when he voted for the Bush-era education reform law No Child Left Behind.

Update 9:36 p.m. ET. On Syria:

Santorum says he doesn't understand why President Obama decided to help in Libya but not in Syria. Santorum says the U.S. has nothing to lose in Syria if the Assad regime is toppled.

But the Obama administration is afraid of Iran, he said, who controls Syria.

Gingrich jumped on it and said that with this president, "As long as you're America's enemy, you're safe."

Romney adds that Syria is a great pawn in relations with Iran. It's an opportunity to put pressure on Iran, said Romney.

Paul jumps in and says the United States simply doesn't have the money to fight another war in Syria.

Update at 9:32 p.m. ET. The Iranians Can't Attack Anyone:

Paul is the only candidate who disagrees on Iran. He says there is no evidence that Iran has nuclear weapons and he adds that the U.S. has Iran surrounded and they "can't attack anyone."

If you want to go to war, he said, at least do it properly. "Ask the people and ask the congress," said Paul. At least get a declaration of war.

Update at 9:28 p.m. ET. On Iran:

Romney says Iran is Obama's biggest failure has been on Iran. "We must not allow Iran to have a nuclear weapon... If I'm president that will not happen. If we reelect Barack Obama that will happen," said Romney.

Update at 9:21 p.m. ET. Women In Combat:

The candidates are asked what they think about moving women into combat roles. Romney said women are capable of those roles. Santorum, in the past, has expressed concern about women serving in the front lines.

Answering the same question, Paul said he doesn't want men or women dying in war.

Santorum said he didn't say women serving in the front lines was wrong. "I said I had concerns."

Update at 9:20 p.m. ET. The Candidates In One Word:

Asked to describe themselves in one word the candidates said:

Paul: "Consistent"

Santorum: "Courage"

Romney: "Resolute"

Gingrich: "Cheerful"

Update at 9:14 p.m. ET. Comprehensive Immigration Reform:

Gingrich says comprehensive immigration reform is impossible. He says Reagan, Bush and Obama were unable to do it, so the only way to go about it is "step-by-step."

"The first step is to control the border," Gingrich said to applause.

Update at 9:10 p.m. ET. On Immigration:

"The right path for America is to drop the lawsuits against Arizona" and others "who are doing the job Barack Obama isn't doing," says Romney about immigration. Romney says states like Arizona are a model of how to deal with immigration.

Update at 8:58 p.m. ET. Planned Parenthood And Contrception:

Santorum is thrown on the ropes first by Paul and then by Romney.

Paul, who has attacked Santorum sharply in previous debates, throws a controversial jab his way saying Santorum voted for Planned Parenthood.

When Santorum tried to defend himself the crowd booed. And Romney jumped in to say that in a YouTube video Santorum praised his vote on Title 10 - which funds programs like Planned Parenthood.

Santorum again got boos for the crowd when he said that he made the video to make the point that while he is against contraception morally, he could put that aside and vote for bills that include it.

Update at 8:51 p.m. ET. A Fractured Family:

Santorum seems to preview how he would handle questions about his comments about birth control and what it is doing for the American family.

"Just because I'm talking about it doesn't mean I want a government to do something about it," Santorum said.

Update at 8:46 p.m. ET. Boos For Birth Control Question:

The crowd boos a question that asks the candidates which of them believes in the use of birth control.

Gingrich, now Romney, are skirting the question by criticizing President Obama and his administration's mandate that religious organizations provide contraceptives to their employees.

Update at 8:44 p.m. ET. Social Issues To Come:

We're at our first commercial break and so far while the debate has been heated, we haven't gotten to the social issues that have dominated the news in the past few days.

Update at 8:34 p.m. ET. On Bailouts:

Santorum is asked about why he opposes the bailout of the American auto industry.

Santorum said he is opposed to public bailouts of private industry in principle. He opposed the Wall Street bailout and the auto bailout, while Romney, he said, supported the Wall Street bailout but he didn't support the bail out for the "people of Michigan."

Romney responded strongly saying there is "no way we would allow the auto industry" to disappear.

Update at 8:27 p.m. ET. Santorum Defends Earmarks:

Santorum says he stands by his defense of earmarks. He said there are some good earmarks, but the system has been abused.

After he finished talking, the crowd was quiet and at least one person booed.

Romney said without uncertainty that he would ban earmarks as president and that led to our first ALERT for the night.

"While I was fighting to save the Olympics, you would were trying to save the bridge to nowhere," said Romney.

Update at 8:19 p.m. ET. 'Because He Is A Fake':

Paul just called Santorum "a fake," saying he finds it curious when candidates first vote for a legislation then run saying they will repeal it. Santorum voted for No Child Left Behind, but now says he would try to repeal it as president.

Update at 8:14 p.m. Romney, Santorum Spar:

As expected, the debate has already featured a lively back and forth between Romney and Santorum. Interestingly, the sparing came on government spending.

Santorum tried to tie Romney to the Occupy Wall Street Movement and said Romney said he would raise the debt ceiling. Romney seemed annoyed, saying he was only for raising the debt ceiling if government found a way to pay for it.

Update at 8:08 p.m. First Question On Debt:

The first question goes to Santorum. An audience member asks the candidates what they will do about the country's debt.

Santorum says under his administration defense would not see cuts, but he would cut entitlement programs which Santorum says are the problem.

Volleying, Romney criticized Santorum's record in Congress saying spending grew while he was Senator.

Santorum defended his record, saying he took on entitlements and never raised taxes.

Update at 8:07 p.m. ET Introductions:

Paul introduces himself as the "defender of the constitution."

Santorum says he's here to talk about a "positive solution" the problems of the country.

Romney says he's the candidate that wants to "restore America's promise."

Gingrich says that he has come up with an energy plan that will allow every American to look forward to $2.50 gas.

Update at 8:06 p.m. ET. The Rules:

Candidates have one minute to answer and 30 seconds for a rebuttal.

Update at 8:02 p.m. ET. Candidates Take The Stage:

CNN's John King will be moderating the debate tonight. He is also introducing the candidates: Gingrich is first on stage, followed Romney, Santorum and Paul.

One interesting change on the stage is that the candidates will be seated tonight.

Update at 7:54 p.m. ET. The Line Up Tonight:

Courtesy of CBS' Political Hotsheet, this is how the candidates will lineup tonight. From left to right:

"Paul, Santorum, Romney, Gingrich. Santorum's got to to feel good about that middle spot"

The New York Times points out that this will be the first time Santorum takes center stage.

Update at 7:39 p.m. ET. Pre-Debate Talk:

Here's a bit of the pre-debate talk on Twitter. Texas Rep. Ron Paul tweets:

"According to Arizona voters, Ron Paul is leading Obama in a head-to-head match up: http://ow.ly/9e2F3"

While Rick Santorum tweets:

"I'm looking forward to sharing my vision for America during tonight's CNN Arizona debate."