Noah Feldman, Tribune News Service

There has been much worried Democratic speculation about how the Supreme Court might intervene to hand the election to President Donald Trump. Many scenarios are possible, but one is much more probable than the others. After Monday’s Supreme Court ruling blocking late-arriving mail-in ballots from being counted in Wisconsin, we can now say very concretely what the Bush v. Gore redux scenario looks like.

The scenario would arise in Pennsylvania. And the decisive vote would likely be cast by Justice Amy Coney Barrett. That’s because of Pennsylvania’s distinctive legal dispute about whether to count mail-in ballots received after 8 p.m. on Election Day.

First, it’s important to understand that a Supreme Court decision about Pennsylvania will only truly determine the outcome of the election if the electoral vote is close enough to make Pennsylvania decisive. If either candidate can win without Pennsylvania, this scenario wouldn’t decide the presidency.

But if the electoral tally is close, and late-arriving ballots in Pennsylvania could provide the margin of victory, we could be in for a legal nightmare.

As I explained in an earlier column, Pennsylvania state law says that ballots can’t be counted if they are received after the polls close on Election Day. But the Pennsylvania Supreme Court, relying on the Pennsylvania Constitution, ruled that under current conditions created by the combination of COVID-19 and US mail delays, the state must count ballots received for three days after the statutory deadline.

When the US Supreme Court was asked to review the Pennsylvania Supreme Court’s ruling, it split 4-4. That Oct. 19 tie left the ruling in place. Neither side issued an explanation until Monday, when the justices gave their reasoning in a similar case pertaining to Wisconsin.

Here’s where things get a little complicated, so stay with me. In the Pennsylvania case, Chief Justice John Roberts cast his vote with the court’s three liberals. His reasoning, we now know, was that it is up to the Pennsylvania Supreme Court to interpret Pennsylvania law, including electoral law and the Pennsylvania Constitution. It’s not up to the US Supreme Court. Hence he voted not to intervene.

In the Wisconsin case, Chief Justice Roberts voted with the other conservatives to block a federal judge’s order that also extended the deadline for receiving mail-in ballots after the statutory cutoff. He reasoned that, unlike the Pennsylvania Supreme Court, which is a state court, a federal district court ought not to change a state’s vote-counting rules.

So the court won’t allow extensions of mail-in ballot receipt deadlines where federal courts might order them. But the court does appear to respect decisions by state legislatures to allow the counting of mail-in ballots received after Election Day. That leaves precisely one unresolved scenario: a state in which the state supreme court has extended the deadline. In other words, Pennsylvania.

Now fast forward to 8 p.m. on Election Day. Assume that Trump is ahead in the vote count in the state. But Biden mail-in votes are still coming.

Trump’s lawyers would no doubt go back to court to demand that state authorities stop counting the late-arriving mail-in ballots. Indeed, they already asked the Supreme Court to reconsider its Pennsylvania ruling. On Wednesday afternoon, the court declined to do so. Barrett did not participate because, a court spokesperson said, she had not had time to review the briefs.

Trump’s lawyers have other options to get back to the court, however. A statement by Justice Samuel Alito that was joined by Justices Clarence Thomas and Neil Gorsuch — but not by Justice Brett Kavanaugh — said that after the election, the court could still agree to hear the Pennsylvania case on an expedited schedule. Alito also invited Trump’s lawyers to ask for a motion requiring the state to segregate the ballots received after 8 p.m. on Election Day so that they could be uncounted after the court heard the case.

The upshot is that Trump’s lawyers could still ask the justices to vote yet again on whether to stay the Pennsylvania Supreme Court’s ruling and stop the counting — thus effectively giving the states electors to Trump. This time the decision would come before nine justices, not eight, because Barrett has now joined the court.

We know that Roberts and the three liberals would vote to leave the Pennsylvania order in place. And we have strong reason to think that the four justices conservatives who already voted to overturn the Pennsylvania Supreme Court’s decision would do so again.

Assuming they do, the deciding vote would be Barrett’s.

What would be best for the republic is obviously for this whole scenario not to arise. So vote, if you haven’t already. And maybe drop off that mail-in ballot yourself, assuming state law allows it. Oh, and one other thing. Pray.