The highest court in the nation is set to rule in a case that could lead to a major shift in how mail‑in voting works across the United States.

In more than two hours of oral arguments Monday, the U.S. Supreme Court debated whether federal law allows states to count mail-in ballots received after Election Day.

Before the Supreme Court is Mississippi's law, which allows mail ballots that are received up to five days after the election to be counted as long as they were postmarked by Election Day.