Mail in ballots are not just a modern dilemma. Even during the Civil War, states were not unified in their practice of allowing deployed soldiers the right to cast their ballots for the presidential election of 1864. Many states refused to allow "mail in ballots" from the field. Ulysses S. Grant in a letter to Secretary of War Edwin Stanton on September 27th wrote "In performing this sacred duty, [solders] should not be deprived of a most precious privilege. They have as much right to demand that their votes shall be counted, in the choice of their rulers, as those citizens, who remain at home; Nay more, for they have sacrificed more for their country" (Chernow 452). Even Grant, Lieutenant General of the U.S. Army was unable to vote absentee due to his own state Illinois not allowing the practice. 

Not really wanting to compare soldiers at war with  the current national/global pandemic, but how do we secure our American democracy in times of crisis?