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Donald Trump may be the loudest voice in the Republican presidential field, but on his heels is the candidate quietly surging to the front of the pack: Ben Carson.

Those spoiling for a fight between the two candidates may be disappointed. Even if Trump attacks, "we have pledged amongst ourselves to not return fire," said Carson's communications director Doug Watts.

As Carson prepares for campaign events in California this week, both he and Trump sit among the top three in the early states of Iowa and New Hampshire. Both are battling for support among two key Republican constituencies: evangelical Christians and Tea Party backers. Yet of all the contenders in the Republican field, only Carson beats Trump in a head-to-head matchup, according to a recent Monmouth University poll.

"We're in his slipstream," said Watts. The slipstream strategy is a familiar one to cyclists and NASCAR drivers: ride in the wake of the frontrunner, who enjoys the lead while still battling the headwind, then pass into first place as the race nears its finish.

"Clearly we're behind [Trump] in the polls," said Watts, "but we are of a similar speed and a similar type of vehicle behind him that carries a lot of the same message."

It may be the same message, but it's delivered very differently. Where Trump is bombastic, Carson is soft-spoken. His low-key style gave even his own advisers pause early in the campaign, though they see it as an advantage now.

Says Watts: "We have a similar songbook. We're just singing in a different key."

Trump has praised the doctor from Baltimore, calling him "a nice guy." But he said on MSNBC's Morning Joe on Friday, "I'm hoping for Ben to really hit me at some point because I love to counter-punch."

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Trump may have to wait a while.

"We intend to be positive throughout the primary campaign," Watts said.

At the moment, Carson is capitalizing on the anti-establishment wave among GOP primary voters. The campaign, which reportedly raised $10 million in the spring and summer, pulled in millions more last month, according to an adviser.

"The interest just continues to rise," said Andy Yates, a North Carolina-based political consultant and executive director of One Vote, a Carson super PAC.

He recalls bigger donors, early in the year, wondering about Carson's credibility as a candidate and whether he could handle the rigors of a presidential campaign. Now? "Those questions have been answered with a resounding yes," said Yates.

Serious questions still exist about Carson's preparedness for the presidency. He's been dogged by his controversial comments on gay marriage and has stumbled in foreign policy discussions — something he addressed in the first Republican debate.

"The thing that is probably most important is having a brain," he said in August, "and to be able to figure things out and learn things very rapidly."

Since that debate, he's seen a steady rise. Carson is up 14% in Iowa since July, according to the latest NBC News/Marist poll, and up 5% in New Hampshire.

His supporters point to steady crowds at Carson events. Upwards of 5,000 attendees are expected at a rally in Anaheim on Wednesday afternoon. Carson's also surging on social media: his Facebook page added 20,000 followers on a single day in September, according to the campaign. (His bus, by the way, dubbed the "Healer Hauler," has its own Twitter account.)

Mindful of the need to set expectations, Carson's communications director cautioned upcoming ad buys by opponents in Iowa and New Hampshire would likely put a dent in Carson's rise.

"We're uncomfortable where we are. We didn't expect to be in quite such a strong position at this point in time, because it raises expectations that are very hard to sustain," said Watts, adding they'd be hard to sustain for any candidate this early in the race.

Still, Carson’s supporters believe he will ultimately rise to the top as an anti-establishment alternative to Trump.

"He's a lot of the things people like about Donald Trump, without the negatives, without the brashness,” said fundraiser Yates.

He added: ""I think you'll see a lot of Trump supporters move to Carson as they start to get tired of the outlandish."