National pols are conducted to determine the popularity or electability of presidential candidates. My understanding is that eligible voters (those who are registered to vote) are the people who are targeted to participate in these pols.
Now since we typically have low voter turn out (30% to 40% I think) in presidential elections polling registered voters is probably not an accurate way to determine who will be elected in the next presidential election.
So, what do y'all think is the real trend for those 30% or 40% who are actually planning to vote in the next election?