"It's possible that consumer trend will recover and get better as the year wears on here, but if it were to be weak, that would negatively affect Apple," Hall said. "We're not saying this is the only data point you ought to be focused on. We just think this it's very interesting that that activity level is down year over year."
To be sure, fewer drivers doesn't necessarily mean fewer buyers, as shoppers continue to move online. This year, both Black Friday and Cyber Monday saw record-setting revenue, lifted by online sales, according to forecasts by Adobe.
An Apple Watch was sold every 13 seconds and an iPhone 7 was sold every 30 seconds in the U.S. on eBay, for instance. And consumer sentiment seems to be holding up for now: The University of Michigan Index of Consumer Sentiment rose to its highest level since January 2015 so far in December.
"E-commerce is certainly taking away from that traffic," Hall said. "And weather has been really on the eastern part of the country through this time of year, so that tends to keep people away from the shopping centers."
Still, e-commerce sales were only about 8.4 percent of total retail sales in the third quarter, the Census Bureau said last month. And JPMorgan's estimates make sense with data from Adobe Digital Insights, which showed a postelection traffic dip at stores.
The stakes are also high, as Apple recovers from three straight quarters of yearly revenue slides. The company's AirPods have already faced delays as the crucial window is closing for Christmas shoppers.
Apple was not immediately available to comment on the report.
The holiday quarter is huge for Apple, with about 78 million iPhones expected to be sold during the quarter, according to FactSet. That's compared to 46 million in the September quarter, and up from 75 million phones a year ago.
Though most analysts expect iPhone 7 sales to rise, Hall said that JPMorgan expects handset sales overall to fall 11 percent compared to last year. Personal computers are even more at risk, and could also see a disproportionate impact from a shopping slowdown, Hall wrote.
"We had been assuming a better trajectory for higher end vendors like Apple," Hall wrote in a research note. "Should consumer spending finish up somewhat sluggish in the US .... this could drive weaker than expected earnings."