In 2015 at the Frankfurt Motor Show, Porsche unveiled its Mission E electric sports sedan, due for the road by late 2019. Although unmistakably a Porsche, the low-slung four-door was clearly aimed at the insurgent Tesla.

With two electric motors producing more than 600 horsepower, the all-wheel drive vehicle was said to be capable of zero to 62 miles per hour in 3.5 seconds, and 310 miles on a charge.

The...