Most national polls are designed to skew toward the demonRATs, and they do it out in the open.
If you poll the country based on population, kalifornikator will get 11% of the calls.
The poll is going to lean demonRAT before the first call is made. The same with NY or IL.
Because there are so many heavily populated states that are blue, a national poll can not be fair or predictive.
It would be more telling to a presidential race to do polls of the rest of the country without California callers or weighting. That would give a better picture as to where the race is really going. You can give poll results both with and without California in the mix.