Clinton's campaigning problems were cobsistent, IIRC, across all of her elections; she consistently lost ground, she just had less of it to lose in her Presidential run. (This is true not only of here Senate and Presidential general election campaigns, but also both Presidential primaries.)

It seems likely to me that it wasn't her pollsters from all those elections that were the weakness, but the candidate, who has a strong loyal base within the party, limited ability to hold on to votes that initially lean her way that aren't part of that base, and basically no ability (in part because of hardened negative opinions on a large segment of the electorate) to swing opposed or uncommitted voters.