Manchester, New Hampshire (CNN)Hillary Clinton, facing a tougher than anticipated challenge for the Democratic presidential nomination from Bernie Sanders, is preparing to take a new look at her campaign structure, she said Monday.

Several people close to the campaign, particularly in Bill Clinton's orbit and among donors, acknowledged discontent within the operation and feel the campaign was too slow to recognize and deal with the threat posed by the Vermont senator.

These concerns were magnified after Clinton eeked out a win in Iowa, carrying the state by less than 1%, and the fact that the former secretary of state is trailing Sanders in polls ahead of Tuesday's New Hampshire primary. According to a CNN tracking poll released Monday evening, Sanders is leading Clinton in New Hampshire 61% to 35%.

People close to the campaign said there will be no firings, but that additional hiring is likely, particularly to beef up the campaign's digital and fundraising arms. Politico first reported Monday on the disarray in the Clinton camp.

Clinton, after a campaign stop in Manchester, responded to the reports of a campaign shakeup in an interview on MSNBC's "The Rachel Maddow Show" Monday, acknowledging her campaign will "take stock" of their operation.

"I have no idea what they're talking about or who they are talking to," Clinton said of the Politico report. "We're going to take stock, but it's going to be the campaign that I've got. I'm very confident in the people that I have. I'm very committed to them, they're committed to doing the best we can."

John Podesta, her campaign chairman, looked to dismiss the rumors, tweeting, "There is zero truth to what you may be reading. It's wrong. Hillary stands behind her team, period."But, according to people close to the campaign, there is dissatisfaction within the campaign, especially from Bill Clinton and his orbit of advisers and donors.

The former president has been concerned that the campaign has shown "a lack of imagination and hasn't been forward looking enough," according to a Democrat who has talked with him.

When asked publicly, the former president has stood by Clinton's campaign aides, even commending some of them on stage at events. But privately, a Democrat close to the former president said Clinton worries the campaign is "playing it safe."

The problem for Clinton, one Democratic strategist with knowledge of the campaign says, is that, in many ways, the die was cast a couple of years ago. The speeches, this source says, are problematic.

"It's not like the ramifications are unforeseeable," this source adds.

Another Democratic strategist familiar with the campaign makes the case that the candidate herself is "not inclined towards simple message repetition."

The message that should be repeated endlessly, this strategist argues, is simple: she wants to level the playing field and lift people's incomes.

David Axelrod, a CNN contributor and former top adviser to President Barack Obama, suggested that the blame lies at the top.

"When the exact same problems crop up in separate campaigns, with different staff, at what point do the principals say, 'Hey, maybe it's US?'" Axelrod tweeted.Sanders has provided Clinton with a stronger challenge than many in Clinton's orbit anticipated and has shown an ability to raise large sums of money online. Sanders raised $20 million in January, a figure Clinton aides worry means he can run a viable campaign into the late spring. By comparison, Clinton raised $15 million last month.

The Clintons have a history with hinting at staff shake ups and campaign realignments.

Patti Solis Doyle, Clinton's 2008 campaign manager, was replaced by Maggie Williams, Clinton's chief of staff when she was first lady, in February 2008 after Obama won contests in Nebraska, Washington state, Louisiana and the U.S. Virgin Islands. Doyle had been with Clinton since she was first lady of Arkansas.

Republicans, meanwhile, are enjoying what they see.

"The Big Dog is swinging for the fences, Clinton is tanking in the polls and falling behind in fundraising, and now her campaign is bracing for a February shake up," Republican Party spokesman Michael Short emailed reporters. "It's 2008 all over again, except this time it's not Barack Obama causing heartburn at Clinton HQ, it's a 74-year old socialist from Vermont."