What’s behind the vote-by-mail controversy in the US?

Voters across the United States are set to take part in midterm elections on November 3. But with two months left until polling day, a major legal battle is taking place that could throw the entire process into chaos. Acting on election fraud concerns raised by President Donald Trump, the US Postal Service (USPS) is scrambling to take steps purportedly to ensure the security of mail-in ballots.

Roughly 48 million US voters cast their ballots through the mail, as of 2024. Critics have warned that restricting the process could disenfranchise groups who rely on mail-in voting ahead of the critical midterm vote. In late August, however, the Supreme Court granted an emergency request to allow the Trump administration to proceed with its reforms.

That has injected uncertainty into the last-minute election preparations, with early voting slated to begin in some states as early as September. On Tuesday, Democratic Senator Richard Blumenthal made public a whistleblower complaint he received detailing problems with the Postal Service’s plans to restrict mail-in voting. What changes are under way?

Why are they happening now? And what lies inside the whistleblower complaint? We unpack that and more in this explainer.

Trump has long claimed, without proof, that his opposition, the Democratic Party, is involved in rigging elections. To justify that statement, he has made two intertwined but unsubstantiated allegations. First, he maintains that Democratic-led states are allowing non-citizens to vote.

Second, he argues that states are not doing enough to secure the millions of mail-in ballots sent out each election season. But experts and election officials have cast doubt on those assertions. Election fraud is incredibly rare, and experts say the few documented instances have not swayed election outcomes.