Presidential candidate Ben Carson at his home in Upperco, Md., on Dec. 23. (Marvin Joseph/The Washington Post)

Three of Ben Carson's high-ranking advisers, including campaign manager Barry Bennett, quit Thursday following an internal power struggle, a sharp decline in the polls and a week of confusion about who would remain on the retired neurosurgeon's presidential campaign team.

"Barry Bennett and I have resigned from the Carson campaign effective immediately," said departed communications director Doug Watts in a statement to The Washington Post. "We respect the candidate and we have enjoyed helping him go from far back in the field to top tier status." Hours later, Carson’s deputy campaign manager Lisa Coen also submitted her resignation.

Armstrong Williams, Carson’s longtime confidant and business adviser, told The Washington Post that retired Army general Robert F. Dees, a campaign foreign policy adviser whom the candidate first met at church this year, would take over as chairman. Senior adviser Ed Brookover, a veteran Republican consultant, will manage the operation. Carson's campaign described these moves as "announced enhancements that will shift the campaign into a higher gear."

“Bob Dees is in charge and Dr. Carson will make that announcement on Monday in Washington,” Williams said in an interview. “Bob is a general. He knows how to manage and run a smooth organization.”

Shake-ups are not that unusual after a campaign starts dropping in the polls. But this one comes a week after the campaign's inner tensions erupted publicly.

At the heart of it were simmering tensions between Bennett and Williams. Bennett, an experienced GOP operative, wanted the campaign to be more traditional in its setup, fundraising and messaging. Williams, who has known Carson for more than two decades, thought Bennett’s approach did not bring out the candidate's strengths.

It was a classic divide between the candidate’s friends and professional aides, with each side believing it was working in Carson’s best interests. Carson, making his first run for office at age 64, has been enamored with the idea that upstarts and non-professionals could upset the political class.

"It is important to remember that amateurs built the Ark and it was the professionals that built the Titanic," Carson tweeted in October. Weeks later, at the fourth Republican debate, Carson falsely insisted that "every signer of the Declaration of Independence had no elected office experience."

Statements like these did not rattle the campaign. The real breaking point came two days before Christmas when Williams and Carson decided together, without Bennett's knowledge, to invite The Washington Post and the Associated Press to Carson’s Maryland mansion to discuss, among other topics, a staff shake-up.

When asked during that interview whether Bennett would stay on, Carson responded: "All of these things are on the table for consideration."

The campaign followed that interview with a confusing statement from Carson that expressed "100 percent confidence" in his advisers. But by then Bennett felt burned by Carson and believed Williams was taking control of the campaign. He also called it a "stupid move" for Williams to urge Carson to talk to reporters about the campaign's unrest.

“I spent the holidays hearing every day that I had lost my job,” Bennett said in an interview Thursday. “My relationship with Carson was always good and friendly, but being campaign manager in that kind of situation, where outside advisers are in essence driving the campaign and setting up interviews and raising questions about everything, it’s not the right atmosphere.”

Just one month earlier, Carson insisted to reporters that Williams had "nothing to do with the campaign." Yet by late December, Williams and Carson had been huddling for weeks, discussing possible changes as Carson’s poll numbers tumbled. Meanwhile, Carson had been holding separate daily conversations with Bennett about tweaking the campaign.

But Williams seemed to outweigh Bennett in the scale of those talks because Carson felt more comfortable with him. As Williams explained in an interview, “I know his heart. I’ll be here whenever it’s over and I was here before it started.”

Bennett informed Carson about his decision Thursday morning in a phone call. They have not seen each other in person since before the holidays in mid-December. Carson had called Bennett from his home in West Palm Beach, Fla., to get an update on fundraising and the campaign.

“It started out like we always start out, ‘Good morning, how are you? How are things?’ Then I said, pretty simply, that I was resigning. He was very surprised. He said, ‘Can you think about it? Can you wait until the end of the day, think it over?’ I just said, ‘No. I’m sorry. I’m done,' " Bennett said. "My point was, you can’t put the genie back in the bottle.”

“I expect lots of other people will resign today as well,” Bennett added. “The divide between the outside and inside is too deep. There is nothing we could change structurally at this point to make it better. It is what it is, Dr. Carson is who he is. I have so much respect for him, but he wants to do things in a way that I don’t, so it’s best that I step down. I’m sure they’ll figure it out.”

Several operatives in early voting states, and Iowa in particular, have charged that the campaign has relied too heavily on organic support and online fundraising without making sufficient attempts to organize that energy in a more tangible way. Others accused the campaign of misusing its funds, reinvesting the bulk of its earnings into raising more money, chartered flights and into bloated campaign salaries instead of building the sort of robust infrastructure in early voting states that will be crucial for whomever locks down the nomination.

When first reached at his northern Virginia office today, Williams said he first heard about the shake-up on Twitter. Then he said he spoke to Carson by phone. “He told me, ‘Barry has made his decision.’ But look, Dr. Carson told you last week that he was going to be making changes. This was always his plan. Didn’t Carson say last week that he was going to shake it up?”

He declined to comment on how money had been spent and said he would refrain from further judgment on how Bennett and Watts performed.

"There’s enough pain today, enough feelings that have been damaged in some ways," Williams said. "I’m already being blamed, as I knew I would be, but I would never criticize Barry and Doug. They did a lot of good for the campaign with social media. I know they will criticize me, but this is a different season, and we wish them well."

According to Williams, Carson had reached his staffing decision by the time he gave the interview to The Post. When asked about Carson's earlier statement of "100 percent support" for his staff, Williams replied,
"his actions today, a week later, tell us what that statement meant. It didn't mean much."

Bennett said he hasn’t ruled out jumping into another campaign, but he first wants to rest.

“Sleep. Sleep. That’s what I’m going to do. I’m very tired," he said. "The internal [expletive] became what the campaign was about. It was sad. Petty. It became mind numbing to me. Having worked so hard on building up the fundraising operation and getting millions behind Dr. Carson so he’d be ready for 2016, I got pulled into this [expletive]. It’s not why I got in this business."

The holiday shake-up also overwhelmed what might have been a good day of news for Carson. Watts's final act was to announce that Carson had raised more than $23 million for the fourth fundraising quarter of the year, ending 2015 with more than 600,000 unique donors and at least 1 million individual contributions.

But the meaning of those numbers had been lost as Carson struggled. In the third quarter, his campaign raised $20.76 million and spent $14.24 million. A full $11.21 million spending had been plowed into further fundraising, as Carson's campaign relied on pricey direct mail to build his list. None of those investments were paying off as the Republican primary's focus turned to terrorism and national security.

"Listen, the world changed after Paris and San Bernardino," Williams said. "Dr. Carson has changed too. I must tell you, I’ve never known him to be more at peace. He’s at peace more than you can imagine. And when he's at peace, I'm ecstatic."

Most Republicans outside of Carson’s campaign reacted to the news with little surprise, chalking up the Carson experience as typical of what happens when a first-time candidate collapses.

“Any time a campaign starts going the wrong way, there is always internal dissent and especially so when the candidate is an outsider and a first-timer,” said Edward J. Rollins, who co-managed Ross Perot’s 1992 presidential bid and Ronald Reagan’s 1984 reelection.

Rollins painted a bleak picture of Carson’s path ahead: “At this point, I think his candidacy is finished. He has money but his staffers are gone and nothing really to keep him going. Iowa isn’t seriously in play, he has no strength in New Hampshire.”

But the campaign turmoil did not appear to spread to the early voting states, where Carson's unorthodox campaign had been organizing for months. In Iowa, where Carson has slipped to third or fourth place after leading some polls, his state director Ryan Rhodes dismissed the staff changes as "a big deal in D.C." and nowhere else.

"I'm excited for the caucuses," said Rhodes. "Ben Carson has promised that we'll have the resources to be successful on the ground. We're organizing and we have all the backup we possibly need."

Jose Del Real contributed reporting.

This story has been updated. It was originally published at 1:30 p.m. ET