But the massive surge in voting by mail doesn’t come without controversy.

For months, President Trump has blasted attempts to increase mail-in balloting, repeatedly warning of “voter fraud” and a “rigged election.” Democrats have pushed back at what they call the president’s “baseless” charges and argue that Trump and the GOP are trying to suppress the vote.

Election experts do say that voting by mail is more susceptible to fraud than casting a ballot in person, but they’ve seen no evidence of widespread fraud or that absentee balloting favors Democrats. But the massive increase in absentee balloting places an extra burden on already stressed-out state and county election officials and on a U.S. Postal Service facing financial and manpower deficits.

Here's a look at which states vote entirely by mail and which states allow absentee balloting without an excuse.

Five states already voted entirely by mail even before the pandemic. Twenty years ago, Oregon became the first state to go to universal mail-in balloting. They’ve been joined by Washington, Colorado, Utah and Hawaii. These states send ballots to all registered voters.