The NBC poll that had the GOP taking a bath oversampled govt workers. Something like 20% of those polled were govt workers vs 8% in the general population. That would make a big difference in the results.
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That would explain the results. Did you get this from the PDF? Is there an R-D-I breakdown?
This is where I saw it:
http://pjmedia.com/tatler/2013/10/10/about-that-nbcwsj-poll-that-killed-republicans-on-the-shutdown/