"What you are seeing is a combination of some of Hillary's soft support shifting and a larger proportion of undecideds going for Obama rather than Clinton," said Bud Jackson, a Washington, D.C.-based Democratic media adviser who is not working for any of the presidential candidates.
"It comes down to electability for a lot of these people. As more undecideds become familiar with Obama and agree with him on the policy issues, they believe he is capable of winning and are more comfortable in supporting him," Jackson told me.
Notably, there is a growing belief inside the Clinton campaign that the media establishment has begun to turn against her. A typical example of this shift was starkly evident this week in a column by Al Hunt, executive editor at Bloomberg News: "The concerns about Clinton ... are that she is devious, calculating and, fairly or not, a divisive figure in American politics. Her once commanding advantage over Obama in Iowa and New Hampshire -- the two critical initial contests -- is evaporating."
This dramatic shift in the way the national press is portraying the New York senator and her campaign forced Mark Penn, her chief strategist, to rush a memo out to her supporters -- acknowledging the race is closer than before but arguing that Clinton is still on course for the nomination.
"No question that this is a fully engaged race, and the polls in Iowa are competitive and tight," Penn said. "But the polls in the other states show meaningful leads as we head into the homestretch, and Hillary maintains a national base in Feb.-5 states that is strong and unmatched."
Still, the decline in her support levels suggests that something deeper is going on among the Democratic base. This week's Gallup Poll showed her dropping from 51 percent in October to 44 percent in November to 40 percent now, while Obama jumped from 21 percent to 30 percent over the same period.
At this rate, with a long 54 days to go before the mega-state primaries on Feb. 5, it is easy to see how the unexpected could happen.