In addition, it’s getting much harder for pollsters to get people to respond to interviews. The Pew Research Center reports that it’s getting only 9 percent of the people it contacts to respond to its questions. That’s compared with 36 percent in 1997.

Interestingly, response rates are much higher in new democracies. Americans, particularly in target states, may be getting poll fatigue. When a phone rings in New Hampshire, it might well be a pollster calling.

Are those 9 percent representative of the larger population? As that percentage declines, it seems increasingly possible that the sample is unrepresentative of the much larger voting public. One thing a poll can’t tell us is the opinion of people who refuse to be polled.

Then there is the problem of cellphone-only households.