Republican Presidential Debate

What the candidates need to do on debate night

Trump's front-runner status put to the test

Big week for Republicans as the candidates take the stage Wednesday in Colorado for the first debate with Donald Trump not the absolutely unchallenged front-runner.

The GOP gathering, hosted by CNBC, comes as Trump has lost his lead in Iowa to Ben Carson and new questions have emerged about former Florida Gov. Jeb Bush's ability to make a move in the race.

Here's a viewer's guide to what each of the top-tier candidates needs to do Wednesday night as we enter the "still early … but not that early" phase of the race for the Republican presidential nomination.

Ben Carson (L) and Donald Trump (R).
Getty Images

Trump: The real estate billionaire has already gone on the offensive against Carson, raising questions about the retired neurosurgeon's Seventh-day Adventist faith—while simultaneously denying doing so. He's likely to keep up the attack on Wednesday, though probably skipping the religion stuff—very dicey territory—in favor of hitting Carson's energy level and lack of business experience.

The debate—focused on jobs and the economy—should play to Trump's strengths. He needs to give his fervent supporters what they want: no holds barred aggression and bravado leavened with humor and occasional self-deprecation. Low energy Trump is not what the "Make America Great Again" crowd wants to see.

Carson: Can he translate his current strong showing in Iowa to other states? Pundits tend not to credit Carson's low-key, soft-spoken style but it plays better with actual voters. And he shouldn't really change it.

But Carson needs to show some steel in the face of likely attacks from Trump and give possible supporters in New Hampshire and elsewhere a better sense of what he would do as president. If the question of his faith does come up, Carson should turn it in an opportunity to further appeal to evangelical voters and contrast himself to Trump, who when asked could not come up with his favorite Bible passage.

Marco Rubio: The senator from Florida performed strongly in the first two debates, helping move into a (quite distant) third behind Trump and Carson. He just needs to do it again with brisk, detailed policy answers while skipping jokes about his water consumption.

Trump will have an easy opportunity to go after Rubio for being a career politician who has never created jobs. Rubio, who has already said he's skipped votes because he dislikes the Senate and will not run for another term, needs to have a pivot ready to his vision for creating faster growth and greater opportunity. Turning to his own family story of rising from humble immigrant roots would be a good way to deflect any attacks on his own lack of broad business experience.

Bush: Supporters of the former Florida governor say they don't expect big changes in his debate approach. Bush is not going to try to out-Trump Trump but rather stick to his line of standing up to the front-runner while focusing on his plans to deliver 4 percent economic growth and more widespread prosperity.

Bush tends to prefer wonky answers, which don't always play well with so many people on the stage and so little time for answers. But with the debate focused on the central theme of Bush's candidacy, he needs to sharpen his delivery and give his strongest performance to date.

It's not at all clear even a strong performance will help with Bush's core problem, the fact that there does not seem to be any market for establishment candidates with famous last names in the current GOP environment.

But the Bush team plan—keep chopping wood and play the long game—remains the same. He has the money and organization to stick around at least until the voting starts. The question is whether the candidate himself gets tired of running in the Age of Trump and decides it's not worth it.

Ted Cruz: The senator from Texas is hanging around with Rubio and Bush in the mid-to-high single digits. But he has shepherded his resources well and has nearly $14 million in his campaign account. And Cruz has assiduously courted Trump supporters in ways other candidates have not, positioning himself to be a potentially big winner if the billionaire eventually fades and gets out of the race.

Cruz must keep that up in the debate while also use his rhetorical gifts to inspire religious voters. It would also be helpful for him to have a breakout moment or two in the debate that will get people talking and lift him into the double-digit range in early polls.

Carly Fiorina: The former HP CEO's bounce from the last debate evaporated quickly. She is likely to be strong again but can expect Trump broadsides against her corporate record. Her talking points on HP and the Compaq acquisition better be razor-sharp once again.

The rest of the field: Hope for a miracle.

Watch CNBC's "Your Money, Your Vote: The RepublicanPresidential Debate" on Wednesday, October 28. The debate will feature two setsof candidates discussing critical issues facing America today, including jobgrowth, taxes and the health of our economy. Coverage begins at 5pm E.T.

—Ben White is Politico's chief economic correspondent and a CNBC contributor. He also authors the daily tip sheet Politico Morning Money []. Follow him on Twitter @morningmoneyben.