I reported on this a while back, and it’s worth repeating. Polls are generally done by telephone. Polssters get lots of answering machines, and hangups. They never call cell phones, only land line phones, and they don’t call unlisted numbers. So, you can see, wide swaths of people get filtered out from pollster phone calls.
There’s lots of people pollsters never speak to, such as people who
1) aren’t home much.
2) use a cell phone as their main phone.
3) let the machine get it.
4) check the caller id before answering.
5) have an unlisted nunber.
6) don’t immediately hang up when getting an unsolicited phone call.
In short, among other groups, they’ve virtually eliminated from their polls, the highly mobile urban population, who might be expected to be more liberal.
No, it’s not a conspiracy, just changing technological times, with the pollsters quite aware of the current shortcomings of their methods – and not sure what to do about it.