But the DCCC has their internal polls too, right?
Yep- I very much doubt that the DCCC would pull out based purely on a NYT poll in what october? With the amount of polling resources, modelling, credit history and just general institutional knowledge they'd base it on a lot more than that.
Going from my experiences with Labour, targeting decisions are made after a rather comprehensive combination of
lots of various data, and general political knowledge.
Besides it was still the right decision by the DCCC- I don't believe that any spending investment of less than 300-500K would have made a big enough difference to cut a 5% margin, especially when the Democrats had a weak candidate