Is vote-by-mail needed to protect the 2020 election?

Wisconsin’s primary election — thrown into chaos by partisan clashes, late-night court decisions and long lines of masked voters — offers a “nightmare vision of what the whole country could see” in November if the coronavirus hasn’t been contained, the state’s Democratic Party chairman said.

Election experts and lawmakers have suggested a variety of contingencies to make sure people are able to vote in this year’s presidential election even if the virus makes lining up at polling places unsafe. A popular solution among Democrats is expanded access to mail-in...