How can a survey with a total of less then two voters per congressional district--most of which are secured to one party or another, so not relevant--get an accurate demographic?
If you include only districts that are "in play", you are likely to strongly skew to one party or another depending on which races you consider "in play".
Alternatively, if you include districts not "in play", then the results are not representative.
Your post is a good reason to end gerrymandering.