NYT:

Just how big a public health emergency the virus will become remains unknown. But the virus is already affecting the primaries in complications for voters overseas, canceled party fund-raisers and polling places that opened late on Super Tuesday because worried poll workers failed to show up. And if the outbreak continues to grow and intensify, or if, like the 1918 influenza, the contagion abates and then comes roaring back in the fall, it may soon be too late to do anything about it before the presidential election.

“The problem is, we don’t have a plan for what happens if a part of the country faces a disruption on a presidential Election Day,” said Rick Hasen, an election law expert at the University of California-Irvine’s law school. He said Congress should right now be considering federal legislation that would address potential voting trouble. “What if one part of the country is affected, if it’s California or Florida?” he said. “The closer we to get to the election, the harder it’s going to be to come up with rules that look fair.”

This was indeed a factor in the 1918 election, which was not a presidential year but was plagued by issues nationwide involving quarantines and emergency measures. Al Smith, running as a Democrat for governor of New York, accused local Republican officials of calling last-minute bans on public gatherings to tamp down his support, rather than to prevent the spread of flu, according to a 2010 study of that election year. The outcome of a local judicial race in Idaho was eventually overturned in part because special arrangements were made to allow a small group of people under quarantine to vote.