In its effort to challenge vote counts in key states, the Trump campaign has filed lots of lawsuits that have little chance of winning. But there is one suit that it should win — not only for the Trump campaign or the 2020 election, but for all elections in the future. It’s the court fight over Pennsylvania’s election rules, and it involves a fundamental issue that is important to all 50 states.

The first thing to remember is that the Constitution gives state legislatures the authority to make rules governing the conduct of elections for federal offices in their state. In October 2019, the Pennsylvania state legislature passed Act 77, which updated and revised the rules. For the first time, it allowed all Pennsylvanians to vote by mail if they chose, without requiring that they show they would be absent from their voting district on Election Day. Remember, this was pre-coronavirus, and Pennsylvania was moving toward greater voting by mail than ever.

On the question of voting by mail, the legislature made one clear, unambiguous requirement: All mail-in ballots had to be received by 8 p.m. on Election Day. (It let stand an existing law that allowed military and overseas ballots to be received for seven days after Election Day.)

Then, in March of this year, after the arrival of the virus, the legislature revisited the law. It made some changes to accommodate voting in a pandemic. It rescheduled the state’s primary election and included measures to help reduce crowding at polling places. But it left untouched the requirement that all mail-in ballots had to be received by 8 p.m. on election night.

That’s where things stood as the presidential election approached. Then a number of Democratic groups filed a lawsuit against the secretary of state. The groups said the pandemic required that the deadline be extended. The case went to the Pennsylvania State Supreme Court, which has a 5-to-2 Democratic majority. On Sept. 17, the court threw out the legislature’s deadline and created a new one: 5 p.m. on Nov. 6, three days after Election Day.

They did not claim that the existing law was unclear. “We are not asked to interpret the statutory language establishing the received-by deadline for mail-in ballots,” the majority justices wrote. “Indeed there is no ambiguity regarding the deadline set by the General Assembly.”

Nor did they claim that the existing law was unconstitutional. Instead, the justices claimed that an “extraordinary situation” existed. They repeated a lot of the fretting Democrats engaged in earlier this year about the post office. And then they declared coronavirus a “natural disaster,” threw out the law, and wrote a new one.

Republicans immediately protested. The Constitution gives the legislature the power to make election law. The court can’t just make up a new law. The matter went to the U.S. Supreme Court, which split 4 to 4 on whether it should intervene. (New Justice Amy Coney Barrett was not on the case.) That meant the court took no action. Pennsylvania would keep accepting ballots for three days after Election Day.

Justice Samuel Alito protested vigorously. “The court’s handling of the important constitutional issue raised by this matter has needlessly created conditions that could lead to serious post-election problems,” he wrote.

So now, with the election over, the issue is headed back to the Supreme Court. And putting aside the specifics of the Pennsylvania situation, the matter concerns a hugely important principle, which is the constitutional authority of state legislatures to make election law for their states.

Other states with no stake in the Pennsylvania results can see that. On Monday, 10 states filed an amicus brief upholding the importance of the constitutional rights of state legislatures.

Who will win? Who knows, but it appears Republicans have a strong case that the Pennsylvania court exceeded its authority.  “This is not some constitutional flight of fancy,” said John Yoo, a Berkeley professor and a former George W. Bush Justice Department official. “Justice Samuel Alito has already made clear his view that the Pennsylvania Supreme Court has violated the Constitution. … If the federal Constitution directly grants those powers to the legislature of Pennsylvania, state courts have no authority to alter state election law for federal office, including the presidency.”

In the end, the case might have no effect on the presidential election results in Pennsylvania. But the issue is who writes the election laws in the states — the legislature, or someone else? The Constitution is clear on the matter, and the U.S. Supreme Court needs to decide.

Byron York is chief political correspondent for The Washington Examiner.