In Michigan, voters complained that they received their ballots just before Tuesday's vote or not at all, raising fears that political pressure could be affecting the U.S. Postal Service three months before the Nov. 3 presidential election. In Kansas and Missouri, many conservatives chose to cast ballots in person despite the possible health risk, some echoing President Donald Trump's unfounded claims that mail voting leads to widespread fraud.

The number of absentee ballot requests broke records in at least two states with primaries on Tuesday, offering further evidence of voters' embrace of mail voting to avoid potential exposure to the novel coronavirus at polling locations. At least 77 percent of American voters will be able to cast ballots through the mail in the fall, according to a Washington Post tracker of state rules.