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AMES, Iowa – The preseason is over for the Republican presidential field. When the top eight declared candidates take the stage at the Stephens Auditorium at Iowa State University at 9 p.m. Eastern tonight, they will be playing for keeps.

With voters anxious about the future of the nation, President Obama already out on the campaign trail (including a Michigan factory stop and another big-buck New York fundraiser today) trying to reverse his lengthy slide in the polls and markets continuing to whipsaw on dire economic news, Republican voters are ready to get serious.

Republicans here in Iowa and around the country are optimistic about their party’s chances in 2012, but they’re also ready to get on with the fight. After months of eyeing the prospects, voters are ready to start making their choices. It’s one thing to indulge a spring fling with a long-shot candidate, but quite another to hold onto that crush into the fall.

Tonight’s debate, sponsored by FOX News, The Washington Examiner and the Iowa Republican Party, comes at a time of great opportunity and potential peril for the GOP.

If they find a nominee who can unite their party and defeat Obama in 15 months, Republicans will have completed a remarkable political rehabilitation that began with the Tax Day Tea Parties of 2009. If Obama is re-elected and delivers on his promises of enforcing his federal health care law, new financial regulations and global warming rules, it’s back to the wilderness for American conservatives.

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But beyond the big stakes for the party and the nation tonight are seven men and one woman who come to the stage with their own baggage, opportunities and needs for this debate.

Here’s a look at the expectations for the field:

Bachmann: The Bar Has Been Raised

“One thing I will guarantee you, President Bachmann will be canceling barbecues if we see the market go down and if we see the jobs report going down.”

-- Minnesota Rep. Michele Bachmann campaigning in Newton, Iowa last week after President Obama held a birthday barbecue at the White House

Here’s a sentence Power Play didn’t ever expect to be writing: The most message-disciplined candidate in the Republican field, by far, is Congresswoman Michele Bachmann.

After a successful launch and exceeding expectations in her debut debate performance, this debate is a make or break moment for her. She’s got the most on the line of anyone on the stage.

Bachmann’s early fame as a freshman and sophomore member of Congress came from a tendency to fly far afield in her remarks. Whether opining on the root causes of homosexuality, saying that the Founding Fathers abolished slavery or calling Barack Obama “un-American,” it was her over-the-top talk show rhetoric that made her the House Republican that liberals loved to hate. That hatred, in turn, established her credentials with conservatives who rushed to her defense.

But aside from one early stumble about New England geography (that’s Concord, Mass., congresswoman), Bachmann has avoided the kinds of distractions that have previously plagued her. When Newsweek called her “The Queen of Rage” last week it seemed not just unfair, but kind of silly. She’s been all poise and polish on the trail.

But with Texas Gov. Rick Perry ready to join the race and Sarah Palin cruising down to the Iowa State Fair in her motor coach, conservative voters are keenly aware that they have other options.

Palin’s surprise presence in Iowa this week may help Bachmann with some voters who see her as a surrogate for their beloved rogue. But Perry is only a threat. With executive experience, unquestioned social conservative bona fides and fewer concerns about general election viability, Perry is appealing to the Republican right. In the latest FOX News poll, Perry finished second to Mitt Romney and nearly doubled Bachmann’s 7 percent score (Palin carded an 8 percent).

Bachmann has put voters at ease with her scripted lines and avoidance of unnecessary controversies. She’s refused to hazard opinions on the causes of gayness, the science of evolution and other topics that used to get her off track and has been relentlessly hammering on the big issues for the country today: the economy and the national debt.

But talking points can only get you so far. Bachmann needs to show that she’s fast on her feet and can really face down Romney in her command of the issues. A stumble or hackneyed phrasing could burst the Bachmann bubble. But if she exceeds the now higher expectations, she could be in the race for the long haul.

Romney: Above the Fray No More

"I want to use my financial resources and my time this time to actually get delegates. Not just straw polls that are nice, but don't get you delegates. So I'm not going to participate in straw polls anywhere in the country.. I've been there, had that experience, learned from it, and we're gonna try and get the nomination this time."

-- Former Massachusetts Gov. Mitt Romney on “Hannity” explaining why he is skipping the Iowa GOP’s straw poll

Mitt Romney has run a nearly flawless campaign to this point. He has abstained from the intra-party sniping of his fellow candidates and focused, as the president would say, like a laser on the incumbent and the economic crisis.

It’s worked wonders as Romney has quietly racked up key support, donations and united the moderate wing of the GOP. His argument is that with his business experience and mellower conservatism he is the perfect man to beat President Obama.

Romney is also trying to avoid the mistakes of his 2008 run when his campaign was engaged in a months-long sniper war with every other Republican operation. John McCain was able to fend off Romney in part because of the resentment toward the Massachusetts millionaire from also-ran campaigns. Anybody but Romney became a rallying cry for anxious McCainiacs.

So Romney has taken a much more benevolent tone, which has been effective when dealing with a field where his steady lead was unchallenged by anyone. But that can’t last forever. Benevolence looks like weakness if you let enough attacks go by.

With Bachmann surging again and Perry set to swagger into the race, Romney looks less like a shoo-in and can’t fall back on Yankee forbearance and shoulder shrugs to answer his opponents’ fusillades. And with the clock running out on several candidates in the field, he will be taking lots of incoming fire tonight. With conservatives pining for an anti-Romney champion, there will be no end to the attacks.

Pawlenty: By the Skin of His Teeth

“What we need in this late hour at a time when our country is sinking, when our country is drowning, is strong leaders who are going to roll up their sleeves and put their shoulders back and their head down and drive this thing to conclusion.”

-- Former Minnesota Gov. Tim Pawlenty campaigning in Iowa

Power Play was tempted to say Tim Pawlenty had the most riding on the debate tonight, but that’s not really fair since everything he does now is a make-or-break moment for him.

His two-year-old presidential campaign is now perpetually dangling over the abyss. He’s got the right policies, the best people and a sound strategy to win the GOP nomination, but he has continued to slide into the back of the pack.

Another bad debate, a loss to Michele Bachmann in Saturday’s straw poll, the loss of a key staffer, a bad fundraising report: any of it could doom his chances.

It is often said that Pawlenty is too vanilla… too nice… too Minnesotan to capture the GOP electorate’s affection. The bigger problem, though, is that he has positioned himself as a more conservative alternative to Mitt Romney who is not quite so over the top as the rest of the field.

Pawlenty is running as a Ford Taurus, a more sensible alternative to Romney’s Jaguar or Bachman’s Humvee. But that has confused voters who are looking for bright-line distinctions about their candidates and sharp contrasts.

Tonight, it’s not just important, as everyone already knows, for Pawlenty to show his combative side with Romney. Pawlenty must also define his brand better and show conservatives that he’s really one of them.

And there’s reason to think he might. You know the lyric: “Freedom’s just another word…”

Paul: Straw Man

“We may do quite well on Saturday. I have no idea, exactly. I don't make predictions. But it's significant. It's significant for me personally. It's significant for our campaign. It's significant for the cause of liberty.”

-- Texas Rep. Ron Paul on the stump in Mason City, Iowa setting the stakes for the Ames Straw Poll

Ron Paul’s needs in tonight’s debate are immediate: He needs a performance that will help him win Saturday’s straw poll.

A win in the straw poll would help reinforce the message that Paul is still the emotional and ideological favorite of the Republican activist community. Conversely, a poor showing in the straw poll, say third or worse, will suggest that the door is closing on 75-year-old Paul’s candidacy.

If Iowa activists are starting to forsake their first love in the name of electability, Paul will start to fade quickly and, so will his platform to share his libertarian message.

Paul has been one of the driving forces in changing the direction of the GOP. The ideas for which he was roundly mocked and berated by his 2008 contenders – a more humble foreign policy, ending the Federal Reserve and even the gold standard – are now very much mainstream Republican ideas.

To keep up that push toward libertarianism, Paul needs to give Iowa activists a reason to give him another boost on Saturday. Expect Paul to pull no punches when it comes to his fellow candidates or his ideas.

Santorum: Veep-ability

“Ron Paul certainly is more of a libertarian, and you have folks like Pawlenty and Romney, who are, I think, more moderate. So I'd say, I'm sort of in the middle of the crowd, if you will.”

-- Former Sen. Rick Santorum striking a moderate posture “On the Record w/Greta Van Susteren

Rick Santorum hasn’t risen or fallen much in his long campaign, making instead steady progress by persuading orthodox Catholics and other religious conservatives that he is fighting for their views.

But that’s not taking him anywhere near the nomination. What Santorum could become would be the right kind of running mate for a Republican nominee who struggles with the religious right (see Romney, whom Santorum warmly endorsed in 2008).

Santorum’s task tonight is to show that he is fierce about his beliefs but not so dogmatic that he couldn’t withstand a general election. He may also look for ways to ingratiate himself to Romney by directing his barbs at others in the field -- maybe highlighting Bachmann’s short political resume or pushing Pawlenty on social issues.

But don’t look for him to join in the attack on Romney.

Huntsman: Who Are You, Why Are You Here?

"On these issues and more, the president has sadly failed us.”

-- Former Utah Gov. Jon Huntsman during a campaign stop in Florida offering his starkest criticism yet for his former boss

Jon Huntsman has a lot of problems as a candidate: low numbers, no identifiable base, constant drama in his campaign team and an unusual two-state strategy (Florida and New Hampshire).

But his biggest problem may be that Republicans don’t know why he’s running or what it is that motivates him. He has been a boutique candidate that appeals to East Coast media types and Republicans who loathe the Tea Party populism that has swept their party, but that’s not going anywhere.

If there is to be any future for a Huntsman campaign, he has to explain to regular Republicans why he wants this job and who he is. The viral approach of dirt bike videos and snarky Tweets may win approving nods from Politico, but it’s not going to shuck much corn in Ames.

Gingrich: Run-on Candidate

“You look at the whole mess over the debt ceiling and you think to yourself, ‘It should be possible for Americans to come together and find a way to do some things.’”

-- Former House Speaker Newt Gingrich, a combatant in two government shutdowns, “On the Record w/Greta Van Susteren”

In debt, down in the polls, without a substantial organization: that’s not how anyone wants to go into a debate.

But, Newt Gingrich has one last chance tonight to get back into the Republican’s conversation and redeem a damaged reputation. Gingrich is a great debater who loves to riff on policy and shred other ideas.

If he can show that he still has lots of ideas and an acid tongue, Gingrich may get what he wants most of all: a chance to be an intellectual force in the GOP.

If he is undisciplined or repetitive as he also has a tendency to be, he will lose out on his chance to be the ideas guy for the GOP. How Gingrich’s run ends matters a great deal for his future relevancy in the conservative movement.

Cain: Liberatingly Low Stakes

"Contrary to what some of the opponents say, it is not regressive on the poor; it actually empowers the poor. They would pay no tax on used goods. They would have no payroll tax coming out of their check ... and they would receive, along with everyone else, a monthly prebate on sales tax for basic necessities."

-- Herman Cain to the Spencer (Iowa) Daily Reporter defending his idea for a national sales tax

Herman Cain will get a lot of tough policy questions tonight, but Power Play isn’t expecting a lot of nitty-gritty policy answers.

Republican voters love Cain’s speaking style, killer one-liners and disdain for professional politicians, but they aren’t looking to him now to tackle the big policy problems.

His ideas are complicated and often fairly radical – national sales tax, eliminating capital gains taxes – stemming from his time as a Federal Reserve board member and businessman.

But that’s not the Cain to watch for tonight. His other professional life, that of talk show host, will be his way this evening. With dimming prospects for nomination and some cruel reductions coming in the weeks ahead, Cain will try to leave ‘em laughing.

And Now, A Word From Charles

“We were talking here about how detached and disengaged he appears and how disturbing it is particularly to Obama's allies in the press. But the irony is that even if he were undetached and concerned and involved, the markets have shown that he is the anti-E.F. Hutton. When he speaks, no one listens. The markets take no notice whatsoever of what he does. And the reason is he has no ideas. He's out of bullets. He's out of arrows. He doesn't have a clue.”

-- Charles Krauthammer on “Special Report w/Bret Baier

***Today on “Power Play w/Chris Stirewalt” at 11:30 a.m. ET: It’s all Iowa, baby. Chris gets down and dirty with Tim Albrecht – who happens to be the chief spokesman for the highest Republican leader in the state – Gov. Terry Branstad. You’ll also get the perspective of Rep. Tom Latham and the latest behind-the-scenes debate preps from Bret Baier. You’ve got to tune it to live.foxnews.com**