New Delhi, Oct. 14 -- On a fine day in Florence, a city an hour's drive from Phoenix, staff at the local voting centre are doing a tabletop exercise, the euphemism to describe training for election hell. The point is to imagine calamities-fire, power outages, bomb threats-then have a Plan B, C and D. Officials have always made some doomsday preparations, but this year's exercise is more thorough, and the range of threats broader. What, for example, should they do if federal law-enforcement agents show up at the polls?

The staff run through the protocols. Monitors from the Department of Justice (DoJ) can stay if they have an official letter, and indeed the government has said 1,000 will be dispatched across the country. Any other agents m...