Here’s some detail about what’s going on with the Pennsylvania case in the U.S. Supreme Court.
The first thing to note is that the U.S. Constitution gives state legislatures the authority to determine presidential election processes, but says nothing about the role of state courts. The extent to which a state supreme court can alter a presidential election process passed by the state’s legislature is something of an open issue. One might be comfortable with a state court’s role in interpreting ambiguous language, while being less comfortable with a state court holding that explicit provisions of the elections law do not apply.
In 2019 the Pennsylvania legislature passed “Act 77” to reform elections processes. Importantly, this was the law that allowed the form of mail-in balloting Pennsylvania now uses. Before Act 77, mail-in voting was limited to people outside of Pennsylvania, or people physically unable to come to the polls.
A different part of Act 77 simply said that all mail-in ballots needed to be received by the county board of elections by 8 p.m. on election night. The law provides no exceptions to this requirement, and does not provide any process to have a court modify this requirement for reasons like a public emergency, natural disaster, etc. It says they must be in by 8 p.m. on election night, period.
Act 77 was the product of a careful compromise, and thus also contains a “nonseverability” provision. This is a provision that basically says that if one part of the law is ruled invalid, then all parts of the law become invalid. As applied to the current context, the argument would be that if the part of Act 77 requiring ballots to be returned by 8 p.m. is ruled invalid, then the part of Act 77 that allowed mail-in ballots in the first place would also be invalid.
The Pennsylvania Supreme Court ruled that there should be an extra 3 days to return ballots because of the surge in mail-in voting due to the pandemic, as well as the inability of the Post Office to deliver all ballots. It made this ruling on an “equitable” basis, which is legalese for “there’s nothing written down anywhere that specifically says I can do this, but the law is supposed to be fair and this is a fair thing to do.” The Court cited the general principle that it should err on the side of votes being counted.
The Republicans are thus arguing that:
(1) the federal Constitution does not let state courts alter a state legislature’s express instructions for how presidential elections be held (might be correct);
(2) the Pennsylvania election law explicitly says 8 p.m. is the deadline, and doesn’t authorize a state court to suspend or modify this provision (this is true);
(3) Act 77’s nonseverability provision means that if the Pennsylvania Supreme Court suspends the operation of the “deliver by 8 p.m.” provision, it must suspend the entire law (including the allowance of broader mail-in balloting). This is at least a reasonable argument;
(4) Voters had around a month to complete and return their ballots, and were specifically warned by the Postal Service to get their ballots in early due to potential processing delays, so any “diligent” voter’s ballot would already be counted.
I agree with the Pennsylvania Supreme Court that given the circumstances in this election, it is in fact equitable and fair to extend the mail-in period for ballots. But I can’t say that the Republican arguments are unreasonable or somehow an illegitimate attempt to “steal” Pennsylvania’s electoral votes. I’m pretty sure that if the shoe was on the other foot, the Democrats would be comfortable making the same arguments. In any event, the U.S. Supreme Court, should it choose, would have at least a logical basis for ruling for the Republicans, which is why this case may be a tough one to win.
Edit: changed original references to “severability” to “nonseverability” to clear up confusion. For reference, this is the actual language from Act 77:
Sections 1, 2, 3, 3.2, 4, 5, 5.1, 6, 7, 8, 9 and 12 of this act are nonseverable. If any provision of this act or its application to any person or circumstances is held invalid, the remaining provisions or applications of this act are void.