Romney, the book says, has become wary of uttering anything near an open microphone after a few gaffes tripped up the campaign's message.
And fear that Romney's membership in The Church of Jesus Christ of Latter-day Saints might hinder the candidate in Iowa's evangelical-dominated caucuses could have blinded his top advisers to Santorum's rapid rise and eventual victory there.
An anonymous aide told the book's authors in December that the "story that hasn't been written" is that Romney hasn't been able to climb above 25 percent in the polls because voters were turned off by the GOP front-runner's faith.
"Part of the reason for the ceiling, quite frankly, is the Mormon thing," the aide said. "If he was even an Episcopalian, he'd be better off today."
A Salt Lake Tribune national poll late last year found that while most white evangelicals and Republicans say they would be comfortable casting a ballot for a Mormon for president, a quarter of the U.S. voters surveyed said the opposite. That mirrors other national polls that have consistently found a minority of voters who are hesitant to back an LDS presidential candidate.
While it remains unclear how much Romney's faith has played into the former Massachusetts governor's tougher losses in Iowa and the South, election results have shown that Santorum, a former Pennsylvania senator, and Newt Gingrich, a former U.S. House speaker from Georgia, have capitalized on the conservative base of the GOP to log their victories.
Even so, Romney has now nabbed half the Republican delegates he needs to clinch the nomination, and observers say it's become mathematically impossible for Santorum or Gingrich to win enough contests to grab the GOP nod without a brokered convention.
The new book, available for Amazon's Kindle but not in paper form, also sheds light on the Huntsman campaign.
In November, during a low point in Huntsman's flailing campaign, the book says advisers had to talk the candidate out of ending his bid for the GOP nomination and mounting a third-party run. Still, aides joked about being able to take vacation in January, hinting that they knew the campaign was doomed.
Huntsman disputes the assertion that he considered a third-party bid and recently told The Tribune that he was ruling out such a race this year but he conceded to the book's authors that he was disillusioned by the process.
" 'This is the best we can do?' I would run through that thought every time I stood on the debate stage," Huntsman told the authors.
Moreover, Huntsman said he was bothered by consultants trying to mold his image and noted that the worst part of the campaign was the "petty betrayals" a point his wife, Mary Kaye Huntsman, quickly noted was directed at McCain, whom the ex-Utah governor had endorsed in 2008.
Backing McCain in the Beehive State, where Romney won nearly 90 percent of the GOP primary vote in 2008, wasn't Huntsman's most politically expedient move. But the then-governor stood by it.
McCain tossed his support to Romney in New Hampshire the day after the 2012 Iowa caucuses, a move that prompted Huntsman to write a quick email.
"You know, for a guy who paid a huge price in my state to support you, the least you could have done I don't care if you support Romney, that's great but just to have given me the dignity of waiting until after the New Hampshire primary," Huntsman said he wrote.
"I didn't mean to offend," McCain reportedly responded. "I hope your family is well."
Abby Huntsman, a daughter of the ex-governor who is acting as his spokeswoman, responded to the Politico book that it didn't capture the Huntsman campaign.
"My dad is looking forward to a book speaking to the substance that will be required to address our nations massive problems," she said Tuesday, "as opposed to the inevitable political theater that plays out in any campaign."