NBC News- Given President Trump's recent comments on about the propriety of counting mail ballots that arrive after election day, here are some things to keep in mind:

There's nothing unusual about counting ballots after election night. Every state does it. Early returns are incomplete. Mail-in, military, and overseas ballots typically aren't fully counted in more than half the states for a few days after poll close.

The vote count doesn't end on election night for another reason. Counties must canvass the returns, which will include adding in provisional ballots and making decisions about disputed ballots. States don't formally declare a winner until the results are certified. In most states, that process isn't over until mid-to-late November.

The Supreme Court has never ruled that only state legislatures can extend the voting deadline. Even so, four U.S. Supreme Court justices and some lower court judges have said in recent weeks that because the Constitution says every state must choose its presidential electors "in such manner as the legislature thereof may direct," only legislatures can alter voting rules. But in the 2000 Bush v Gore case, that notion attracted only three votes and was not a holding of the court.

In a 2015 case, the Supreme Court said that the Constitution's reference to "legislature" in a separate but similar clause meant the entire lawmaking apparatus, not simply the two statehouses. If the Pennsylvania late-ballot fight comes back to the Supreme Court, this will be a major issue.