5 things to watch for at tonight’s Republican presidential debate

Ten Republican presidential hopefuls will line up onstage Wednesday night for their third debate, but a few key matchups and moments will probably determine the outcome. Here are five competitions within the competition to watch for:

Donald Trump vs. Ben Carson: Until recent attacks by Trump, the two outsiders who lead the polls have laid off each other. But Trump loves being top dog, so his performance after falling behind the mild-mannered retired neurosurgeon will be telling — as will voters’ reactions.

Trump trails Carson in at least four recent polls of voters in Iowa, and a CBS/New York Times poll released Tuesday showed him slightly behind Carson nationwide. Trump has a history of lashing out against his rivals, but rarely on matters of substance. Instead, he takes issue with their looks or their mannerisms, or calls them names. If Trump takes this tack against Carson, he could turn off voters who give the physician high praise for his calm, genteel manner. Over the weekend, Trump took a shot at Carson’s Seventh-day Adventist religion, also a risky strategy.

A safer path for Trump might be to continue to challenge Carson on Medicare. Carson has struggled to explain how his healthcare plan, which centers on health savings accounts, could be paid for without harming the huge government program for retirees that is extremely popular among most Republican voters.

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Jeb Bush vs. Marco Rubio: The two Floridians — onetime allies turned rivals — were destined to clash. And given the current dynamics of the race, it could come to a head during this debate. Bush is flailing in the polls, cutting costs and trying to reassure anxious donors, while Rubio is striving to position himself as an attractive alternative for establishment voters.

Bush needs to establish himself as the preferred candidate for such voters, and a standout performance at the debate could help. Bush’s allies have made clear they see Rubio as his chief competition and have sought to focus attention on the senator’s lack of experience.

“There’s not a lot there, record-wise,” Bush’s longtime strategist Mike Murphy said in a recent interview with Bloomberg. Murphy is running the super PAC backing Bush’s campaign. “Marco’s always had incredible possibilities. But he needs more time to reach them. Because we look at his record, I think we’re finding what the American voters are, that there’s not a lot. He hasn’t done much,” he said.

Rubio holds small leads over Bush in recent national and Iowa polls. But the first-term senator has been skipping his day job to campaign and raise money across the nation and is likely to be challenged on his spotty voting and attendance record.

Ted Cruz vs. Rand Paul: Cruz, the Texas senator, has raised $26.5 million to date and has begun to move upward in Republican polls in early states. A tea party favorite, Cruz is working to consolidate support among various factions of GOP voters. He hopes to pick up supporters of Trump or Carson if either falters. He is courting the evangelical voters who powered the Iowa caucus wins of former Arkansas Gov. Mike Huckabee in 2008 and former Pennsylvania Sen. Rick Santorum in 2012. And he is trying to line up the support of libertarian-leaning voters who backed former Texas Rep. Ron Paul’s presidential bids. Those voters were supposed to be the foundation for his son, Rand Paul of Kentucky, whose campaign is sputtering.

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Carly Fiorina: The former Hewlett-Packard chief and the sole woman in the GOP field drew support with standout performances in the last main Republican debate and in the August undercard. In last month’s faceoff at the Reagan library in Simi Valley, Fiorina’s steely response to Trump’s criticism of her looks was a breakout moment. But she has seen her subsequent surge in the polls and the buzz around her candidacy fizzle recently.

Fiorina will aim to deliver another winning performance, but will be fighting the many other candidates who are seeking their own breakthrough with voters. She’s also open to attacks from her rivals about her controversial tenure at Hewlett-Packard, a topic that they — aside from Trump — have studiously avoided.

The rest of the field: For candidates polling in the low single digits, an attention-grabbing moment could be key to remaining relevant. One of the easiest ways to get attention is to go on the attack, and some are telegraphing their potential targets. Ohio Gov. John Kasich is livid about Trump taking credit for Ford’s decision to return some production to the U.S. from Mexico. The automaker decided in 2011 to move some truck production to Ohio, lured by tax incentives backed by Kasich and other state leaders.

Huckabee has grown increasingly critical of candidates who would modify Social Security or Medicare. Bush and Rubio are among the GOP presidential hopefuls who have called for overhauling such programs for future retirees.

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