Here are a few theories.
A more likely culprit than the role of race in the New Hampshire election was the “likely voter” modeling, with pollsters perhaps over-counting the boost of enthusiasm among Obama supporters following his victory in Iowa. Another possibility is that independents opted at the last minute to participate in the Republican primary, depriving Obama of crucial voters.
A further potential source of error stems from New Hampshire ballot rules. In previous contests, the state rotated candidate names from precinct to precinct, but this year the names were in alphabetical order, with Clinton near the top and Obama lower down. Stanford Professor Jon Krosnick, a survey specialist and expert witness in a lawsuit about ballot order in New Hampshire, has estimated a three percentage point or greater bounce for a big name candidate appearing high on the ballot. Therefore, if pre-election polls randomized candidate names, as most do, they would have underestimated Clinton’s support by at least three points.
Tim Russert reportedly said internal campaign tracking polls were as wrong as the public ones. Obama’s people were telling him he had a 14 point edge; Clinton’s were telling her he was ahead by 11.
Another underestimated factor — a frequently underestimated factor: Early absentee ballots. How many Democrats cast their ballots before the Iowa results? Hillary’s campaign emphasized rounding those up.
Anyway. As I said earlier, Obama needs to be tested while the public’s watching. Recovering from unexpected disappointment is a good next test.