Imagine that 15 million people are essentially off-limits to pollsters because of the hurricane, because they are without power, displaced from their homes or otherwise are well-adjusted human beings who are more interested in looking after their families than in answering a political survey. The Northeast is Democratic leaning, of course: imagine that these voters would prefer Barack Obama to Mitt Romney by a net of 20 percentage points, on average.Fifteen million Americans represent about one-twentieth of the American population. If one-twentieth of Americans, who are 20 points Democratic-leaning, are unable to reply to surveys, Mr. Obama’s standing in the polls would be negatively impacted by a net of one percentage point as a result.