If you’re not weighting by party affiliation it doesn’t matter when or if you ask the question of party preference.
Now that I know Gallup doesn’t weight by party affiliation I understand their poll a lot better.
You need to compare the party affiliation cited by respondents, to the known party affiliation numbers in the population. That way, you can make the adjustments (weighting, after the fact being the usual way to do this) to make the sample more representative of the population being polled. WriteOn and marktwain have it right.
Mr. Newport is referring to another technique for attempting to match a sample to the population — by asking for party affiliation first. That way, they could balance the sample by calling until they had sufficient Republicans (or independents, or whatever they were short of). They would only interview people, if they were affiliated with the underrepresented party. They don’t do that — fair enough. However, they should have made the mathematical adjustments, as described in my first paragraph.
Polls weight by standard demographics -- race, age, gender, income, education, etc.
And, in doing so, they are obviously over-weighting their polls toward Democrats. And it won't be over-weighted by black Democrats...or Hispanic Democrats. It is, instead, by elimination, white Democrats -- at the expense of white Republicans.
The cause of this phenomenon is equally easy to determine: Only 9% of all random phone calls result in an interview. Obviously, white Democrats are significantly more likely to pick up the phone and submit to a polling interview than are white Republicans.
Net:net, the polls are right, as far as they go -- but they are not necessarily representative of the final turnout figure. But you can adjust them to whatever turnout model you want.