GEOFF BENNETT: Good evening, and welcome to the "NewsHour."

The U.S. Supreme Court today rejected a controversial legal theory that state legislatures have almost unlimited power to decide the rules for federal elections and draw partisan congressional maps without interference from state courts.

The so-called independent state legislature theory regained attention after the 2020 presidential election, when then-President Donald Trump's allies raised it as part of an effort to reverse the election outcome.

Chief Justice John Roberts wrote the opinion for the 6-3 majority in this case known as Moore v. Harper, which stems from a dispute in North Carolina.

Roberts was joined by Justices Sonia Sotomayor, Elena Kagan, Brett Kavanaugh, Amy Coney Barrett, and Ketanji Brown Jackson.

Neal Katyal is the former acting U.S. solicitor general.

He argued the case before the court and joins us now with more on the impact of this ruling.

Neal, thank you for being with us.

NEAL KATYAL, Former Acting U.S.

Solicitor General: Thanks for having me.

GEOFF BENNETT: So, this case had to do with gerrymandering.

But how does this ruling, as you see it, go beyond that, and potentially protect the integrity of future elections?

NEAL KATYAL: The facts of this case, you're right, are limited to gerrymandering, but the holding of the case is a widespread, thorough repudiation of this independent state legislature doctrine, Geoff.

And that was the doctrine being pushed by the Republican Party to say, for all voting choices, not just redistricting or maps, but polling places, absentee ballots, everything, the Republican Party said, all of that is up to the state legislature, and the state legislature alone, that they could be even acting unconstitutionally against their own state constitutions, and there would be no check on that, the state courts had no business reviewing that.

That's what we argued against.

That's what the Supreme Court in a very strong 6-3 decision said we were right about, ordinary checks and balances, the American system.

GEOFF BENNETT: After the 2020 presidential election, the Trump campaign and its allies filed and lost more than 60 lawsuits at the state level aimed at overturning the election outcome.

Had this legal theory been legal and actionable back then, what would have been the impact?

NEAL KATYAL: The 60 cases and the 2020 election that were decided against Trump really do illustrate the dangers of this independent state legislature theory.

It would have meant most those cases couldn't have been decided by courts at all, that it will be up to raw political power and what state legislatures do and want to do, with no check or balance, so much so Geoff, that is Trump people even tried to do, say to state legislatures, you can throw out the popular vote altogether and install your own folks before the electorate -- before the Electoral College and send your own votes to -- instead of the popular vote.

So this was a really radical theory.

It was a theory that was defended at the Supreme Court by none other than John Eastman, who was the architect of a lot of President Trump's January 6 policies.

And I'm very pleased to see the Supreme Court rejecting it 6-3.

To me, this decision is a signal that six justices, a solid six justices, are going to stand against monkeying and games and shenanigans in the 2024 election.

GEOFF BENNETT: Well, tell me more about that.

What message does it send that John Roberts, the chief justice, authored the opinion, and that two of the justices that Donald Trump nominated, Brett Kavanaugh and Amy Coney Barrett, joined with the majority in rejecting this legal theory that Trump and his allies pushed and promoted?

NEAL KATYAL: It's a thorough repudiation of the independent state legislature theory, an opinion authored by the chief justice, who's certainly no liberal, joined by Justice Kavanaugh, not a liberal, joined by Justice Amy Coney Barrett, again, not a liberal.

It's a demonstration that law and our history and our tradition of checks and balances still has resonance.

And I do think this will go down as one of the chief justice's finest opinions, if not his finest.

GEOFF BENNETT: The court, in effectively preserving the status quo today, Neal, in your view, is that sufficient?

Are those good enough guardrails in preventing another well-coordinated effort to overturn a future presidential election?

NEAL KATYAL: No, not at all.

So, certainly, the court today took an important step by preserving the 200-year tradition of checks and balances and judicial review over state legislation over elections.

But remember, Geoff, it was 10 years ago this week that the Supreme Court struck down the key provisions of the Voting Rights Act of the Constitution, and the Voting Rights Act, the 1965 Voting Rights Act, saying it was unconstitutional.

That's really opened the door to a lot of gamesmanship at the state and local level.

GEOFF BENNETT: Neal Katyal.

Neal, thanks for your time, as always.

We appreciate it.

NEAL KATYAL: Thank you so much for having me.