Story highlights Several people close to the Clinton campaign said it was too slow to recognize and deal with the threat posed by Bernie Sanders

Clinton is facing a a tougher than anticipated challenge from Sanders

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.

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