First, an article in Gawker reminds us that if you ask people a question, the majority of people will answer, with certainty, no matter what the state of their actual knowledge might be:
PPP surveyed over 1,000 registered voters total, and of those people, an alarming number were not just suspicious but confident that man with too much skin Ted Cruz was, in fact, the Zodiac Killer.
Second, a very serious article in the New York Times explains that the accuracy has gone and nobody is real sure it's ever coming back:
Election polling is in near crisis, and we pollsters know. Two trends are driving the increasing unreliability of election and other polling in the United States: the growth of cellphones and the decline in people willing to answer surveys. Coupled, they have made high-quality research much more expensive to do, so there is less of it. This has opened the door for less scientifically based, less well-tested techniques. To top it off, a perennial election polling problem, how to identify “likely voters,” has become even thornier.
...
Our old paradigm has broken down, and we haven’t figured out how to replace it. Political polling has gotten less accurate as a result, and it’s not going to be fixed in time for 2016. We’ll have to go through a period of experimentation to see what works, and how to better hit a moving target.
Also, this by Jill Lapore in The New Yorker:
Still, data science can’t solve the biggest problem with polling, because that problem is neither methodological nor technological. It’s political. Pollsters rose to prominence by claiming that measuring public opinion is good for democracy. But what if it’s bad?