Sept. 6 (Bloomberg) -- Having avoided preemption by a presidential address, the debate of hopefuls for the Republican presidential nomination looms tomorrow night as a critical event on the party’s primary calendar.

All eight candidates are under pressure to perform, yet that pressure isn’t evenly distributed, and the participants don’t all have the same burdens and opportunities on debate night. So who has to do what to be a winner at the Ronald Reagan Presidential Library in Simi Valley, California?

Although many have suggested that Texas Governor Rick Perry -- participating in his first debate of the race -- has the most work to do, in fact, just the opposite is true. Perry does have a long way to go before his front-runner status is cemented, but in this debate, he needs to establish only one thing: sure-footedness.

No candidate since Wesley Clark in the Democratic primaries in September 2003 has leapt so quickly from entering the race to the front of the polls. As the debate-preparation coordinator for the Clark campaign, I remember those heady and anxious days. Like Clark in the fall of 2003, Perry in 2011 is drawing support from many voters who have never heard him utter more than a sound bite or two -- a tenuous position.

Perry’s mission tomorrow night then, is to do nothing that unnerves these newly acquired supporters in their first extended exposure to him. He must sound sharp on economic matters and reassuring on national-security concerns. Having come so far, so fast, Perry probably cannot -- and almost certainly need not -- gain ground in the debate; his focus needs to be on making sure he doesn’t make major gaffes that imperil his status.

Practice, Practice, Practice

If I were advising Perry, I would have him off the campaign trail, preparing, resting, and practicing, practicing, practicing.

By contrast, the performance burden falls most heavily on the previous front-runner, former Massachusetts Governor Mitt Romney. In the months before Perry got in the contest, the Romney campaign lost its edge by adopting the political equivalent of a prevent defense in the first quarter of a football game. Unprepared for what hit them, the Romney camp has floundered since Perry came on the scene.

Romney has lurched to the right, in a doomed effort to compete with Perry and Representative Michele Bachmann of Minnesota on their turf. As a result, he is losing the “strength” primary to Perry, as the Texan appears comfortable with his more natural positioning, while Romney seems uncertain and weak in his newfound conservatism. Romney needs to use the debate to reclaim the middle ground, showing that he can stand up to Perry and Bachmann instead of trying to emulate them.

Outrageous Statements

Perry has made outrageous statements, even by the standards of the Republican primary electorate. In his 2010 book, “Fed Up,” he suggests that Social Security is a program “violently tossing aside any respect for our founding principles,” and that Medicare is unconstitutional. This should be fodder for Romney at the debate for a much-needed move to unapologetically reassert a centrist position for his candidacy.

Only by taking on Perry’s extremism can Romney arrest his opponent’s momentum. Will Romney be the 2012 version of Arizona Senator John McCain -- the 2008 front-runner who stumbled early but regained his footing -- or will he more closely resemble former New York Mayor Rudy Giuliani, the early leader in 2008 who saw that position slip away, never to be reclaimed? That question starts to be answered tomorrow night.

Establishing Competence

Bachmann, too, finds herself under pressure, albeit for a very different reason. She has raised the bar for herself with her success in earlier debates: Mere competence (what Perry must demonstrate in his first outing) won’t be enough to ensure a successful night for Bachmann. Unlike Romney, who needs to aim his fire upward at Perry, Bachmann needs to take her shots at two candidates who are nipping at her from behind: former executive Herman Cain and Texas Representative Ron Paul.

For while Bachmann will ultimately have to counter Perry’s gains among establishment conservatives, her most immediate concern should be the fracturing of grass roots, Tea Party support among herself, Cain and Paul.

She should use the debate to appeal to these voters directly, telling activists that their failure to unite behind a single candidate means the inevitable nomination of either Perry or Romney. She needs to make the case for why she -- and not Cain or Paul -- is the right wing’s best chance at having one of their own as the Republican candidate.

Breakthrough Moment

Former House Speaker Newt Gingrich and former Utah Governor Jon Huntsman are rarely lumped together, but they share a common task tomorrow: avoiding irrelevance. Thus, the preparation that most candidates engage in for debates -- polishing expertise, crafting answers, preparing for oddball questions -- is of no importance to them.

A good overall performance does little for them; what each of them needs is a single, exceptional, breakthrough moment. With Perry, Romney and Bachmann hogging the spotlight (on the one hand), and Cain and Paul sustained by hard-core followers (on the other), Gingrich and Huntsman need to use the debate to avoid a Tim Pawlenty-like fade into oblivion. Their goal is to claim an attack, a new slogan, a memorable idea that cuts through the clutter and earns them precious post-debate sound bite coverage that will otherwise go entirely to the big three.

They won’t get many chances, and they can’t wait until the setup is just right: They need to force their moment as soon as they get the microphone.

Core Supporters

Cain and Paul, by contrast, need to do only what they do best: energize their core supporters. Unlike Gingrich and Huntsman, who are failing to find an audience, Cain and Paul have devoted followers who seek out what their candidates are saying even when the mainstream media gives them little airtime. Yes, they need to guard against any effort by Bachmann to snatch their supporters, but their best counter to such an effort is to stick with the messages that have won them a devoted following.

If all the other candidates need to stretch in some way on debate night, Cain and Paul just need to keep firing up their supporters with uncompromising, hard-line positions that lack broad appeal, but resonate with true believers. And what about former Pennsylvania Senator Rick Santorum? He should just enjoy his time in the limelight, which is probably coming to an end soon.

Perry, Romney and Bachmann enter the debate like stock cars on the track, running three abreast down the straightaway, speeding toward a corner.

Will Perry spin out? Will Romney reclaim the middle of the road? Can Bachmann put distance between herself and Cain and Paul?

Something -- someone -- is going to have to give ground in Simi Valley.

(Ron Klain, a former chief of staff to Vice President Joe Biden and senior adviser to President Barack Obama on the Recovery Act, is a Bloomberg View columnist. He is a senior executive with a private investment firm. The opinions expressed are his own.)

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To contact the writer of this article: Ron Klain at rklain@bloomberg.net.

To contact the editor responsible for this article: Max Berley at mberley@bloomberg.net.