There may be an additional factor as well. Presidential campaigns, national parties and individual candidates each have overlapping ground operations. But a big, big part of that mix is driven by the presidential campaign. We're accustomed to presidential races where the campaigns have at least broad parity. On any given Sunday the worst team in the NFL might beat the best. They're broadly comparable. But the Trump campaign's field operation might be more like a pro football team squaring off against a high school squad or no team at all. We just don't have any track record for a competition that mismatched.
Case in point (from Eric Levitz):
Clinton has led Trump in 10 of the last 11 polls of the Sunshine State; she is outspending him over the airwaves $51 million to $30 million; she has 68 offices in the state to his 29: and she has nearly erased the GOP candidate’s traditional advantage among absentee voters.
But the lion’s share of Trump’s troubles are self-created. The GOP nominee’s limited presence on both the ground and airwaves are a product of his refusal to put as much effort into fundraising as Romney did four years ago. And his Florida campaign got off to a late start by every metric: Two-thirds of the campaign’s TV ads just started airing this month, all but one of his Florida offices opened after September, and his absentee-ballot-“chasing” operation only kicked into full gear after Democrats briefly overtook Republicans in the mail-in vote last week.