Staff departures in early states have underlined growing pains as what was once a shoestring operation has become a 200-plus person machine, causing Sanders' world to expand beyond the loyalists who have been with the liberal icon for more than three decades -- with the attendant personality conflicts.
Since the first Democratic debate last month, Hillary Clinton has rebounded in the polls, most notably in New Hampshire and Iowa. She's done it in part by appealing to the liberal base by opposing the Trans-Pacific Partnership and the Keystone pipeline -- and hitting Sanders for past votes against gun control measures.
And his campaign's plan to win support with black voters, leaning on surrogates like veteran liberal academic Cornel West and Black Lives Matter activist Symone Sanders, has yet to pay off -- symbolized by the largely white makeup of his audiences, even when he's appealing to a black audience.
It isn't all bad news for Sanders, however. Nina Turner, a top official in the Ohio Democratic Party, announced Thursday that she was withdrawing her support for Clinton and taking a leave of absence to campaign for Sanders. The departure, a surprising one that has Ohio Democrats seething, is notable because Turner was an early backer of Ready for Hillary, the super PAC that preceded the Clinton campaign.
Sanders says he's not worried.
"We started this campaign at 3% in the polls. We're now either winning or doing very well in a number of states. We have more individual campaign contributors than any candidate in history at this point in the election. We have hundreds of thousands of volunteers. And we're taking on somebody who is universally known," Sanders told CNN this week. "I'm feeling quite good about where we are."
Sanders and team say they haven't changed his somewhat unorthodox debate preparation, which looked more like a cram session before the first debate.
Sanders, members of his family and aides will arrive in Iowa on Friday, but instead of holding events leading up to the debate, the senator plans to lay low in Des Moines, much like he did in Las Vegas last month. Sanders had a fairly pithy assessment of his preparation after a brief talk before striking government workers outside the U.S. Capitol this week.
"My debate prep today is to stand with workers who are trying to get a living wage from a contractor with the United States government," Sanders said. "That's the kind of debate prep that inspires me."
Clinton's recovery is a problem Sanders' campaign has been unable to adequately address. Her well-reviewed debate performance was followed a week later by a marathon performance in front of the House Benghazi panel. When Sanders went after her at the Jefferson-Jackson Dinner, traditionally not a place for negative campaigning, she had a sharp and effective retort to Sanders, accusing him of sexism.
At the same time, Sanders was making the pivot from revolution to campaign: building staff, plotting an on-air course in early states and testing out some hits on Clinton.
Jeff Weaver, Sanders' campaign manager and a longtime aide and confidant, said it may look like Sanders is stalling in that transition, but it's only because Clinton was in free-fall this summer. "Internally, it doesn't look like we are losing momentum," Weaver said. "What you are reacting to is the fact that Secretary Clinton's campaign was in free-fall over the summer and now she has been able to stop her downward momentum."
The summer was about building Sanders' name identification and generating energy, he said -- and could be easily replicated.
"If I sat down with my scheduling and advance people today and put together a five-city tour in five days, I could generate mammoth crowds in five different states," Weaver said. "We could do that."
Delay and turmoil
As Sanders' chances of winning the White House grew larger in the fall, the outsider candidate made a number of glaringly establishment moves.
Sanders, who regularly blasts poll-tested politicians, hired a pollster
of his own in late October, weeks after the first debate. With that information the campaign then cracked open its much-vaunted online fundraising operation to lay down $2 million worth of advertising in early states
, their first of the contest.
Some moves carry a lot of promise. The campaign has been pulling Sanders' wife, Jane Sanders, into the spotlight more often to help humanize perhaps the grumpiest candidate running in either party.
"I tell him all the time, you have to bring it back to the hope at the end," Jane Sanders
told CNN's Gloria Borger this week. "But no, he is not grumpy really, just except when the media doesn't pay attention."
Sanders' groundwork courting organized labor also paid off Thursday when he won the support of the American Postal Workers Union, his largest union endorsement and a check on Clinton, who has gained the backing of the American Federation of Teachers and the American Federation of State, County and Municipal Employees.
The Sanders team has promised that Symone Sanders and West would help deliver black support for him. At a September campaign event at Benedict College, a historically black college in South Carolina, West even introduced him as "brother Bernie Sanders
But the chasm between Clinton and Sanders in most South Carolina polls has remained just that -- a massive divide, which Clinton is easily winning with overwhelming support from black Democrats.
Meanwhile, promised domination in New Hampshire and with unions has yet to materialize, leading the campaign to explain it away as Sanders having low name identification, an argument mirrored by flailing campaigns in the Republican field.
But there have also been episodes where it appeared Sanders was in one place while his aides and broader campaign were elsewhere.
Sanders' top strategists and advisers told CNN after October's debate that their candidate had finally agreed to outline his views on democratic socialism in a speech before the second debate. That speech has yet to be scheduled.
Two of Sanders' top staffers in early states left the campaign unexpectedly. Andrew Springer, the former South Carolina communications director, split last week to pursue journalism in West Virginia, his home state. And Jim Farrell, one of Sanders' first staffers on the ground in Nevada, left the campaign earlier this month, citing family reasons.
And then there was the episode where Sanders' top strategists -- Tad Devine and Weaver -- told Bloomberg News they would be "willing to consider" Clinton for the role of vice president in Sanders' administration, a remark that Clinton surrogates blasted.
Sanders wasn't happy. "You know, I think that every campaign has statements come out which are inappropriate," Sanders told MSNBC
. "That was inappropriate."
Trouble hitting Clinton
The most noticeable changes have been Sanders' steady hits on Clinton -- after promising he wouldn't go negative during the campaign -- which have also proved to be the trickiest maneuvers for Team Sanders.
He has made none-too-subtle references to Clinton, without naming her directly, saying she was a latecomer to opposing the Keystone XL pipeline, a core issue for most liberal Democrats, and switched positions on the Trans-Pacific Partnership trade deal -- joining positions Sanders has long held.
Sanders has consistently said he is not attacking Clinton, only setting up aggressive contrasts with his chief opponent. But one quip -- intentional or not -- was put right back in Sanders' face by Clinton to great effect. Pressed during the first debate about his positions on gun control, Sanders complained about all the "shouting" about guns.
Clinton used the opening to accuse him of sexism -- and fundraise off his comment, too.
Meanwhile, Sanders is not hitting Clinton on her emails, her greatest weakness. He said again this week he had no regrets
about handing her that "damn emails" pass at the first debate.
Sanders' remark to Clinton that Americans were "sick and tired of hearing about your damn emails," may have won for the best line of the first debate, but Clinton won on every other metric -- something that doesn't seem to have shaken the Sanders team.
The next challenge
The second debate will test Sanders yet again -- not as a first-timer on the big stage, but for his ability to handle incoming fire.
It is a near certainty that Sanders will take incoming fire from both Clinton and former Maryland Gov. Martin O'Malley, who has recently added Sanders knocks to his stump speech.
At a Democratic forum earlier this month, O'Malley said Sanders needs to answer for saying that a liberal Democrat should challenge President Barack Obama in 2012. That is certain to come up again and while Sanders' aides said he is preparing for the attack line, they wouldn't detail how he plans to rebuff the struggling former governor.
"Wait and see," Weaver said. "I encourage you to watch the debate."