At my local YMCA, one of the guys I hang out with in the weight room does polls for a living.
I asked him, “Why are pollsters usually so wrong about political stuff?”
He told me “A lot of pollsters ask the wrong people the questions. For example, let’s say that I want to know who is going to be the president the next election. Before I ask you who will you vote for, I will first ask you these questions:
Did you vote in the 2016 election? Did you vote in the 2012 election? Did you vote in the 2008 election? Did you vote in the 2004 election?”
He went on to say, “Only if someone tells me they have voted for the last four presidental elections will I ask them who they intend to vote for in the coming election.”
Made sense to me, and explains why all these online polls are lousy.