In a major election-year ruling that immediately sent shockwaves through Washington, the U.S. Supreme Court held Monday that states may count mail-in ballots postmarked on or before Election Day—even if those ballots arrive afterward.

The 5–4 decision marks a dramatic setback for President Donald Trump, the Republican National Committee, and conservative groups that had pushed to force states to reject late-arriving mail ballots, even when voters mailed them on time.

At the center of the case was Mississippi’s law allowing absentee ballots to be counted if they are postmarked by Election Day and received within five business days. Republicans argued that federal law setting a single Election Day meant ballots must be received by the time polls close.

The Supreme Court disagreed.

Writing for the majority, Justice Amy Coney Barrett concluded that federal election law determines when a vote must be cast—not necessarily when a mailed ballot must physically arrive at an election office.

Chief Justice John Roberts joined Barrett, along with the Court’s three liberal justices, forming a rare cross-ideological majority on one of the most explosive voting-rights questions of the year.

Justices Clarence Thomas, Samuel Alito, Neil Gorsuch and Brett Kavanaugh dissented.

The ruling protects similar ballot-counting rules in multiple states and prevents a last-minute election scramble just months before the 2026 midterms.

For voting-rights advocates, the decision is being celebrated as a crucial defense against disenfranchising voters because of mail delays outside their control.

For Trump and his allies, it is a bitter defeat in their broader campaign against mail-in voting.

The decision lands at a politically charged moment. In recent days, Trump’s administration has faced backlash over efforts to pressure states for voter data, while Postmaster General David Steiner sparked alarm by suggesting the Postal Service could refuse to deliver mail ballots in states that failed to comply with proposed federal rules.

A federal judge had already blocked parts of that plan, warning that Trump’s election order raised serious separation-of-powers concerns.

Now the Supreme Court has delivered another blow.

The ruling also comes as Trump has repeatedly attacked mail voting, calling it vulnerable to fraud, despite voting by mail himself in past elections and despite election experts consistently saying documented mail-ballot fraud remains rare.

The political stakes are enormous.

In close races, late-arriving but timely postmarked ballots can matter. Military voters, elderly voters, disabled voters, rural voters and people living in areas with unreliable mail service are among those most affected by strict receipt deadlines.

Had the Court ruled the other way, states across the country could have been forced to rewrite election procedures under intense time pressure before November.

Instead, the majority chose stability.

But the narrow 5–4 split shows just how fragile that stability may be.

The dissenting conservatives warned that counting ballots after Election Day could undermine public confidence and create confusion about final results. Critics of that view argue the real danger comes from rejecting lawful votes simply because the mail system moves slowly.

The ruling will now become a central flashpoint in the fight over the 2026 midterms.

Democrats are expected to frame it as a victory for voters.

Republicans aligned with Trump are likely to use it as proof that stronger federal election restrictions are needed.

Trump has already been pushing for sweeping election changes through proposals like the SAVE America Act, which would reshape voting rules nationwide. Monday’s ruling may intensify that fight.

For election officials, however, the decision offers something more immediate: clarity.

States that allow ballots to arrive after Election Day, so long as they were mailed on time, can continue using those systems without suddenly throwing out thousands of votes.

For voters, the message is simple but powerful.

If your state allows it, and your ballot is postmarked by Election Day, your vote can still count.

That sentence alone explains why this ruling matters.

It is not only about Mississippi.

It is not only about Trump.

It is about whether a voter who follows the rules should lose their voice because a ballot truck arrives late.

On Monday, by the narrowest possible margin, the Supreme Court said no.

And in a country already bracing for another bitter election fight, that answer may echo all the way to November.