As Clinton's poll numbers go down in both Iowa and New Hampshire, her campaign is faced with a potentially big dilemma. On the one hand, as this diary by markw suggests, the Clinton campaign will want to begin setting up a narrative where even IF she loses Iowa and New Hampshire, she can still win the primary.
This narrative won't simply write itself -- the Clinton campaign will have to actively create it. But creating this narrative now will also exarcerbate her problems IN Iowa and New Hampshire. The voters in these states don't want to be told that their votes don't count, just as voters outside of these states might be turned-off by any attempt to spin defeat in Iowa and/or New Hampshire too much.
So Hillary's problem boils down to this: The worse she is doing in polls in Iowa and New Hampshire, the more she will want to suggest that these states don't count for everything. But the more she suggests these states don't count, the worse she will do in polls in Iowa and New Hampshire. It's sort of a vicious cycle.