The court heard arguments in a case from Mississippi that also could affect voters in 13 other states and the District of Columbia, which have grace periods for ballots cast by mail. An additional 15 states that have more forgiving deadlines for ballots from military and overseas voters also could be impacted.

A ruling is expected by late June, early enough to govern the counting of ballots in the 2026 midterm congressional elections.

The court challenge is part of Trump’s broader attack on most mail balloting, which he has said breeds fraud despite strong evidence to the contrary and years of experience in numerous states.

Several conservative justices gave voice to some of Trump’s complaints. Justice Samuel Alito wondered about the appearance of fraud in situations where “a big stash of ballots” that arrive late “radically flipped” an election.

Defending the state law, Mississippi Solicitor General Scott Stewart pointed out that the Trump administration and its allies in the case have yet to submit a single case of fraud due to late-arriving mail ballots.

The court’s liberal justices indicated they would uphold state laws with post-Election Day deadlines.

“The people who should decide this issue are not the courts, but Congress, the states and Congress,” Justice Sonia Sotomayor said.

Forcing states to change their practices just a few months before the election risks “confusion and disenfranchisement,” especially in places that have had relaxed deadlines for years, state and big-city election officials told the court in a written filing.

California, Texas, New York and Illinois are among the states with post-Election Day deadlines. Alaska, with its vast distances and often unpredictable weather, also counts late-arriving ballots.

Lawyers for the Republican and Libertarian parties, as well as Trump’s administration, are asking the justices to affirm an appellate ruling that struck down a Mississippi law allowing ballots to be counted if they arrive within five business days of the election and are postmarked by Election Day.

Justices worried over the slippery-slope problems that could arise no matter who wins the case.

Ballots could be received until the start of the next Congress, two months after the election, Justice Neil Gorsuch suggested.

On the other side, Justice Elena Kagan said the logic of the challenge to late-arriving ballots also would be used to rule out early voting and absentee ballots.

Limits on early-voting also seemed to bother Chief Justice John Roberts, who seemed the conservative member of the court most likely to side with Mississippi.

The court also grappled with whether state laws allowing for late-arriving ballots from military and overseas ballots could survive.

Last year, Trump signed an executive order on elections that aims to require votes to be “cast and received” by Election Day. The order has been blocked in pending court challenges.

At the same time, four Republican-dominated states — Ohio, Kansas, North Dakota and Utah — eliminated grace periods last year, according to the National Conference of State Legislatures and Voting Rights Lab.

The issue at the Supreme Court is whether federal law sets a single Election Day that requires ballots to be both cast by voters and received by state officials.

In striking down Mississippi’s grace period, Judge Andrew Oldham of the 5th U.S. Circuit Court of Appeals wrote that the state law allowing the late-arriving ballots to be counted violated federal law.

Oldham and the other two judges who joined the unanimous ruling, James Ho and Stuart Kyle Duncan, all were appointed by Trump during his first term.