Voting by mail would become much more difficult, if not impossible, for tens of millions of Americans if the U.S. Postal Service is allowed to implement a restrictive rule governing mail voting that President Trump has demanded. The effects would likely be greater for Democratic voters, who vote by mail in higher numbers than Republicans, and in states where mail voting is universal or nearly so. Mail voting may not happen at all in states that resist the Trump administration’s demands for voter data.

The rule would particularly affect people in rural areas and older voters, who tend to cast ballots by mail in greater numbers. It could also deeply affect states where some of the most competitive races for House, Senate and governor will determine control of Congress and state governments. Michigan, where 37 percent of votes were cast by mail in 2022, would be one epicenter, with hard-fought statewide contests and multiple battleground House races.

California, which mails ballots to all voters, is expected to be central to Democratic efforts to win a majority in the House. The rule is being challenged in several lawsuits, and it is on hold temporarily following a federal judge’s ruling on Thursday. The administration is appealing.

Even if the Postal Service is permitted to proceed, it is unclear that it would have time to implement the plan ahead of an election that is fewer than 70 days away. For instance, the rule requires states to upload a list of voters to a federal mail ballot portal that is not yet online. Nearly two dozen Democratic-led states and Washington, D.

C., have sued to block the proposed rule and said they will not comply with it. If the agency were to move ahead, state and local officials would shoulder enormous costs in what would need to be a herculean effort to prepare election offices and educate voters in time for the midterm elections in November. The most dramatic aspect of the proposed rule is a plan to deny services for election mail entirely in states that do not turn over voter data, which federal officials say they want to use to identify noncitizens on state voter rolls.

The policy would upend mail voting in any state that does not comply, but the effects would be measurably greater in the smaller number of states that rely heavily on mail voting. More than one in three Democrats voted by mail in 2024, compared with about one in four Republicans, according to estimates by the States United Democracy Center, which examined voting data in 32 states where it was available. "It’s not that complicated," said Marc Elias, the Democratic election lawyer, who said the new policy was a blatant effort to disenfranchise Democrats. "The administration knows that Democrats are more likely to vote by mail than Republicans. Donald Trump has demonized voting by mail and made that differential even greater."Election administrators fear chaos It is far from certain that the rule could be implemented this year, given outstanding legal and logistical challenges with fewer than 10 weeks before Election Day.

North Carolina, where a highly competitive Senate race could help determine control of the chamber, is set to mail ballots to some voters starting next week. More states will soon follow. President Trump, who voted by mail himself in Florida’s primary this month, created the current uncertainty by signing an executive order in March that called on the Department of Homeland Security to compile state-by-state citizenship lists that could be used to help determine voter eligibility.

Last week, the Supreme Court ruled that the lawsuit was premature because the Postal Service had not yet finalized its rule. Now that the agency has done so, though, and a lower court has weighed in, the justices will likely be asked to rule.