Why the Supreme Court let some states count mail-in ballots received after Election Day but not others - CNN

In North Carolina, ballots can arrive up to nine days after Election Day; in Pennsylvania, ballots can arrive up to three days late -- for now; and in Wisconsin, the court said ballots must be in by election night.

The court made clear that federal courts shouldn't interfere to change state election rules so close to the election.

"The Constitution provides that state legislatures -- not federal judges, not state judges, not state governors, not other state officials -- bear primary responsibility for setting election rules," Gorsuch wrote.

Pennsylvania: Mail-in ballots can arrive up to three days after Election Day -- for now

In Pennsylvania, the circumstances were different, and the case came up to the court twice.

Unlike Wisconsin, where the lower court challenges played out in a federal court, here a Pennsylvania state Supreme Court decision was central to the challenge.

That state court had allowed mail in ballots to count if they are received within three days after the election -- even without a legible November 3 postmark.

"There is a strong likelihood that the State Supreme Court decision violates the Federal Constitution," Alito said.

If that line of reasoning prevails -- that state courts are usurping the authority of state legislatures to set the rules -- it could have vast post-election consequences when it comes to ballot counting and other disputes.

North Carolina: Mail-in ballots can arrive up to nine days after Election Day

The court rejected two exceedingly complicated challenges brought by the Trump administration, Republicans and state legislators, letting stand an accommodation allowing ballots to arrive up to nine days after Election Day, so long as it's postmarked by November 3.