Five things to watch in GOP debate

BOULDER, Colo. - Ben Carson, having risen to the top of a national poll, is about to confront his first big test as a Republican star Wednesday night as the presidential nomination race begins a new, crucial phase.

Ten leading contenders will debate for two hours at the University of Colorado's Coors Events Center. CNBC will host this week's debate, billed as "Your Money, Your Vote: The Presidential Debate on the Economy."

The candidates at 8 p.m.: Donald Trump, Ben Carson, Marco Rubio, Jeb Bush, Carly Fiorina, Ted Cruz, Mike Huckabee, Chris Christie, John Kasich, Rand Paul. The candidates at 6 p.m.: Rick Santorum, Bobby Jindal, George Pataki,

For the first time since Donald Trump's dominant rise over the summer, Carson on Tuesday was leading a national poll, supported by 26 percent of Republican primary voters, compared with 22 percent backing Trump, according to the CBS News/New York Times poll. Florida Sen. Marco Rubio was the next-closest candidate, at 8 percent.

The results, within the poll's margin of error, mark a turnabout from early this month, when Trump led Carson, 27 percent to 21 percent.

As the candidates jockey for support and with the first-in-the-nation Iowa caucuses less than 100 days away, here are the stakes:

Ben Carson. The retired neurosurgeon is this month's one to watch. He has jumped ahead of Trump in Iowa and "his support is very broad," said Ann Selzer, a Des Moines-based pollster. But while he led the CBS/New York Times survey released Tuesday, the lead was narrow and the poll found big majorities of Republicans had not completely made up their minds.

Wednesday, Carson faces a new and perhaps daunting challenge. Trump has begun criticizing him, and others are likely to join in. Carson usually dismisses the barbs in his gentle, quiet way. But the public is still learning about Carson, and traditionally, negative information helps define little-known candidates - and can sink them.

Donald Trump. The real estate mogul's summer of triumph is turning into an uncertain fall. He can no longer promote himself as the clear front-runner, and his numbers have barely moved for some time.

His biggest need at the debate will be to regain some momentum and broaden his appeal by getting more specific about his plans for governing. It will be hard, because his negatives are unusually high for a major candidate. Trump has gotten attention at past debates because of his quips and insults. This time he is likely to be asked for specifics, particularly on his tax plan. Unveiled last month, it would lower individual and corporate income taxes.

Jeb Bush. His lackluster campaign and often bland style have cost him. It's too early to count Bush out, since he and his supporters have raised more than $100 million, and Bush has a battle-tested political network.

He needs to stand out Wednesday. Watch for an issue - perhaps immigration, perhaps taxes - where he can talk with authority about what he did in Florida, where he was governor, and what he would do as president.

Marco Rubio. The senator from Florida is behind Trump and Carson in most national polls yet seen as positioned to become the mainstream voters' front-runner.

Rubio, 44, the youngest Republican candidate, needs to show some gravitas and overcome his lack of government experience. His lagging attendance in the Senate is also raising scrutiny.

Carly Fiorina and John Kasich. Fiorina was a star of the first two debates, but any momentum has fizzled amid questions over her comments on Planned Parenthood. Kasich, the governor of Ohio, got some attention in New Hampshire but has also stalled.

The potential for Fiorina to shine Wednesday night is probably higher, particularly since Hillary Rodham Clinton has solidified her status as the Democratic front-runner and Fiorina has been a sharp Clinton critic.

"When Republicans see her, they like her," Stuart Rothenberg, a nonpartisan political analyst, said of the former Hewlett-Packard CEO.

The rest. Since economic issues are expected to dominate the discussion, Sen. Rand Paul of Kentucky is well-positioned for a decent night. He's been an outspoken Federal Reserve Board critic, charging that it "is now in every nook and cranny of banking with unprecedented regulatory powers and no congressional oversight."

Others will hope to break through. Sen. Ted Cruz of Texas is trying to woo a constituency busy flirting with Carson and to some extent Trump. Gov. Christie is aiming for a breakthrough in New Hampshire, a week after the Iowa caucuses, while Mike Huckabee, the former governor of Arkansas, seeks a similar opening in Iowa.

Their biggest challenge could be getting noticed. At the last debate, Christie went 32 minutes without being called on.