For political surveys, census bureau data provides a starting point and a series of screening questions are [sic] used to determine likely voters. The questions involve voting history, interest in the current campaign, and likely voting intentions.
Well, that's not polling likely voters. That's polling people who SAY they are going to vote. Likely voters are voters you KNOW voted recently, say in 2014 or 2012.
Polling such people is very expensive, which is why they don't do it.
The polls are not reliable because you can count on only about 30% of the population to tell the truth unfailingly.
The rest of you are liars, and you have the government you deserve. You lie, and you elect liars.