A heated court fight over Pennsylvania mail ballots will determine who wins the election. And the decision could well ripple beyond 2020.

The fight isn’t over the presidency, of course — Joe Biden is clearly the president-elect — but a state Senate seat in Western Pennsylvania that hinges on just a few dozen votes.

At its narrowest, Ziccarelli v. Allegheny County Board of Elections is an argument over 2,349 mail ballots cast in Allegheny County that arrived in time but lacked dates filled out on the envelopes. Those ballots, including 311 votes in the 45th Senatorial District, gave incumbent Sen. Jim Brewster, a Democrat, the win by just 69 votes. The state Supreme Court affirmed Allegheny County’s decision to count the votes.

But the district crosses into Westmoreland County, one of the counties that decided not to count ballots that lacked dates, classifying them as incomplete. That creates an unfair situation, Republican challenger Nicole Ziccarelli argued in her federal court lawsuit. Similar votes are being handled differently in different counties, which she says violates the U.S. Constitution’s equal protection guarantees.

“Based on the Pennsylvania Supreme Court’s judgment, mail-in ballots will be counted or not counted based solely on the happenstance of which county election board reviews the ballot,” she wrote in her complaint late last month.

The real impact of the case, experts said, could be much broader than who wins the seat, possibly clarifying a recurring question that has proven hard to answer in the messy real world: When is it OK for counties in the same state or electoral district to have different policies and run their elections differently?

In that vein, the case, which is being heard in U.S. District Court, has the potential to reignite questions and issues raised in one of modern election law’s most momentous decisions: The 2000 U.S. Supreme Court ruling in Bush v. Gore. There, the court stopped the December recount in Florida, ensuring President George W. Bush’s election, after concluding that the state’s patchwork of policies was unconstitutional in treating voters differently depending on where they lived. Different counties, looking at ballots with the same exact issues, would come to different decisions on whether to count them.

Avoiding such conflicts could become particularly important as Pennsylvania continues to change its electoral system. Questions about mail ballots and how they are administered, processed, and counted, for example, take on much higher importance when the number of ballots suddenly balloons into the millions. Other changes, such as new forms of early voting, could present new questions — and counties might answer them differently.

“We need guidance. We need more court decisions clarifying the boundaries of Bush v. Gore, otherwise these issues are just going to continually arise,” said Richard H. Pildes, a law professor at New York University who specializes in election law. The Western Pennsylvania case “definitely has the potential to provide important insight.”

The question of uniformity

County governments manage elections in Pennsylvania, so some degree of difference across the Commonwealth’s 67 counties is normal. While the Pennsylvania Department of State provides oversight and guidance, counties make their own decisions on all sorts of issues, such as where to set up polling places, the format of ballots, or what voting machines to use.

The question is when, exactly, the differences are too big.

Since 2000, the issue of uniformity in election administration has evolved, sometimes in conflicting or confusing ways, said Michael T. Morley, a law professor at Florida State University.

“Can different counties within a state treat materially identical envelopes differently?” said Morley, who this week published a law review article examining all 471 federal and state court rulings through June of this year that cited Bush v. Gore. “Courts have come to different conclusions on that.”

Questions around mail ballots and how to count them are likely to continue popping up as voting by mail takes on a major role in Pennsylvania elections. This is the first year any voter was allowed to vote by mail.

“Sometimes you really are venturing into new turf. Some clarity on this would be welcome,” said Adam Bonin, a Democratic lawyer in Philadelphia who is not on the Ziccarelli case. “I can’t say how often it will ever come up — this could be a once-in-a-decade thing — but it’s always good to have guidance.”

After all, only about 5% of voters in any Pennsylvania election cast ballots by mail in the past, but this year millions did, and the state is still going through the growing pains some other states already went through years ago. With more mail ballots being cast, chances grow that they could determine the outcome of close elections.

» READ MORE: Joe Biden won 3 of every 4 mail ballots in Pennsylvania. Trump won 2 of 3 votes cast in person. What does that mean for the future?

That said, this particular case could be resolved in a narrow way, on one technicality or another, providing little information for the future. And the specific factual circumstances are in some ways unique and won’t be replicated in the future.

State election law says voters “shall” fill out the voter declaration on the envelope, including dating and signing it. The state Supreme Court split on what that meant, with three of the seven justices saying that means ballots must have dates to be counted and that the Allegheny County votes should be thrown out; three justices said undated ballots should be counted.

The tiebreaker, Justice David Wecht, said the law requires ballots to be dated, but that the undated ballots should be counted in this particular election, avoiding penalizing voters.

What will happen in this race?

Ziccarelli has asked the federal judge to find that Allegheny and Westmoreland Counties are creating an equal protection violation and that the solution is to reject Allegheny County’s undated mail ballots. That would give her a 20-vote win.

Of course, there’s another way to make the two counties level, in which Ziccarelli would lose: Count the undated Westmoreland County ballots. There are only a handful of those, not enough to change the result.

That, naturally, is what Democrats would like to see happen, if the judge agrees that the counties have to treat their undated ballots the same way.

“All Westmoreland had to do was follow the Supreme Court [decision] and there wouldn’t be any disparity,” said Cliff Levine, a Democratic lawyer representing Brewster and the state Democratic Party.

And if Ziccarelli loses in court and the ballots remain in the count, Brewster’s win stands.

“This is a real, honest-to-goodness issue,” said Matt Haverstick, a Republican lawyer from Philadelphia representing Ziccarelli in the case. “Those votes matter.”

It’s unclear what will happen when senators are sworn in Jan. 5. The federal case will still be ongoing at that time — U.S. District Judge J. Nicholas Ranjan has scheduled briefs to be due Jan. 8 — and ultimately, who wins the seat might not be the most important thing to come out of the election.

“This is an interesting Bush v. Gore issue,” Pildes said. “It will be helpful for the system as a whole going forward to have some definitive resolution.”