I'm guessing that if the number of electric cars surged by 25% for a few days, it would be much less of a problem.
[0]: http://www.kgw.com/news/eclipse/gas-shortages-long-waits-rep...
Some parts of the US aren't able to easily meet energy demand they can forecast when it goes up by amounts like 25%. For instance, Pepco pays to install thermostats where they can turn down/off your air conditioner[0]. Same with Dominion Energy[1]. I would be unsurprised if an influx of people of the size to cause gas shortages would also cause problems for electrical grids in many parts of the country.
[0] https://energywiserewards.pepco.com/md/faq/index.php#q2
[1] https://www.dominionenergy.com/home-and-small-business/ways-...
My company maintains an old boiler from the 1880s connected to a steam engine/generator from the 1920s. Because we have it maintained and can start it up with 12 hours notice the power company gives us a substantial discount on our power. I understand we actually did turn it on about 5 years ago when something major happened to the grid. We were able to power our [small] town alone. This is one of the least efficient power plants in the country and thus one of the most expensive.
With no electricity, gas can not be pumped from the tanks.
Even when it can, there is immediately a line-up of 100s of vehicles.
(I see this very often in West Africa)