The Supreme Court upheld a Mississippi law Monday that allows mailed ballots to be counted if they were postmarked by Election Day and received within five business days.

The big picture: The justices’ ruling could protect voting in states with similar laws this November and is sure to feed President Trump’s frequent criticism of voting by mail.

• The Trump administration backed the law’s challengers, arguing that allowing states to count ballots received after Election Day undermines the integrity of federal elections.

Driving the news: The court ruled 5-4 to uphold Mississippi’s law, with Justices Samuel Alito, Clarence Thomas, Neil Gorsuch and Brett Kavanaugh dissenting.

• Mississippi Secretary of State Michael Watson defended the state’s ballot law, arguing voters need to make their final choice by Election Day, even if officials received the ballot days later.

Catch up quick: Federal law sets the Tuesday after the first Monday in November as Election Day, language the 5th Circuit Court of Appeals seized on in ruling against Mississippi’s law.

• However, “[t]he electorate’s choice is made when voting is complete, not when ballots are received,” Barrett wrote in the majority opinion.
• Military and overseas voter advocacy groups had warned a decision siding with the 5th Circuit could exacerbate “already significant barriers” to voters abroad.

Zoom out: The decision is part of a trio of blockbuster election cases the Supreme Court decided or is set to decide this term, along with its narrowing of a landmark voting rights law and a pending decision over a major GOP challenge to campaign finance restrictions.

Go deeper: Supreme Court’s final cases loom over Trump’s immigration, election hopes