A stunning split decision at the Supreme Court may be the most significant election case of 2020

On Monday, the U.S. Supreme Court issued what may be its most significant decision involving the 2020 election, and the Democratic Party should be pleased. But there are still reasons for consternation.

Splitting 4-4, the court left in place the Pennsylvania Supreme Court's decision to extend the deadline to receive mail-in votes until Nov. 6, three days after Election Day. As long as ballots are postmarked by the end of voting on Nov. 3, and received by the 6th, election officials will count the vote.

Court watchers had noted that the decision was taking longer than expected, leading to extensive speculation about the backroom machinations. Surprisingly, there was no long dissent or other written opinion that would explain the delay. Chief Justice John Roberts joined with the three liberals on the court in favor of leaving the extension in place, and the four other conservatives voted to overturn it. Many pointed out that were Judge Amy Coney Barrett a Supreme Court justice, as she is expected to be confirmed shortly, she would likely have sided with the other conservatives and flipped the result of the ruling.

But since the court was evenly split, the Pennsylvania court's decision stands.

This is potentially significant for several reasons. First, Pennsylvania is rated by FiveThirtyEight to be the state most likely to be the "tipping point" state in 2020 presidential election. That means if the race comes down to a single state's vote, that state is most likely Pennsylvania. Second, extensive polling shows that Democrats are far more likely to be voting by mail than Republicans are. Giving voters more time to get their ballots in and have them count makes it more likely that Democrats, and former Vice President Joe Biden in particular, will prevail in the election.

Republicans brought the challenge to the Supreme Court, arguing that the states' supreme court had overruled the legislature's decision to set its elections laws. Democrats opposed this challenge, arguing that the state supreme court has protected Pennsylvanians' right to vote. Law professor Josh Douglas argued that the conservatives' vote to hear the case and possibly overturn the state court's ruling could undermine the very idea of states having their own constitutions.

Some even warned that the votes counted after Election Day may not end up counted anyway, if Republicans take their challenge back to the Supreme Court once Barrett is confirmed. However, it's not guaranteed that even the four conservative justices would vote the same way if they consider the case again.