WASHINGTON — The Supreme Court on Monday removed President Trump's travel ban from its October calendar, an indication that it may have just gotten harder to challenge. But that won't stop opponents from trying.

By adding and subtracting affected countries after a 90-day review, the ban against certain travelers from eight countries in three continents could strike federal judges as less discriminatory than Trump's first two versions, legal experts said.

But by making the prohibitions indefinite rather than temporary and continuing to target mostly Muslim nations, the ban still provides plenty of fodder for the states, led by Hawaii, and immigration rights groups challenging it in court.

What seems clear to both sides in the wake of Trump's unveiling of Travel Ban 3.0 Sunday is that the current Supreme Court case has been altered, perhaps fatally. What's left is for the justices to get new briefs from both sides by Oct. 5 before deciding its ultimate fate.

"The parties are directed to file letter briefs addressing whether, or to what extent, the proclamation issued on September 24, 2017, may render cases No. 16-1436 and 16-1540 moot," the court said in its order.

"I think the court should and will dismiss the case as moot." said Stephen Legomsky, professor emeritus at Washington University School of Law and a former top immigration lawyer at the Department of Homeland Security. "The new proclamation changes both the factual and the legal issues."

Trump's first travel ban, issued in January, targeted seven predominantly Muslim countries: Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen. His second, issued in March, eliminated Iraq and allowed exceptions for legal permanent residents and those who already had visas. That didn't impress two federal appeals courts, but the Supreme Court in June allowed much of the ban to go into effect.

The new version subtracts Sudan and adds Chad, North Korea and Venezuela. Chad is 53% Muslim. North Korea sent fewer than a dozen immigrants to the United States last year, challengers said. The ban on Venezuela affects only some government officials and their families.

"Adding North Korea and Venezuela provides some cover. It makes it look less like it was just aimed at Muslims," Douglas Laycock, a law professor specializing in religion at the University of Virginia Law School, said. But because of the small numbers affected, he said, "the cover is looking very thin."

Anthony Romero, executive director of the American Civil Liberties Union, which has one of the two cases pending at the Supreme Court, said "President Trump's original sin of targeting Muslims cannot be cured by throwing other countries onto his enemies list.”

The key to the legal process may hinge on what procedure the administration used to devise the new list of countries and the particular restrictions placed on each. Federal law gives the president authority to exclude travelers if the basis is not discriminatory.

"No one ever contested that the government has the power to restrict immigration for legitimate national security reasons," said Stephen Vladeck, a professor at the University of Texas School of Law specializing in national security issues. "The question all along has been whether the reasons are legitimate, and that terrain, obviously, has now shifted a bit."

Challengers to the first two bans insist they still have a potent case. "This has not changed anything about the road to the Supreme Court," said Zahra Billoo, executive director of the Council on American-Islamic Relations' San Francisco office. "For us, this was a Muslim ban, and it remains a Muslim ban."

Much of the constitutional argument that the ban violates the First Amendment's freedom of religion has hinged on Trump's comments during the presidential campaign and his many tweets since taking office. Most recently, the president said the ban "should be far larger, tougher and more specific" — presumably referencing the new version he unveiled just days later.

Justin Cox, a staff attorney with the National Immigration Law Center, one of the principal challengers to the ban, said the case remains potent because the administration has yet to demonstrate that existing vetting procedures are inadequate.

"We're not going anywhere," he said in reference to the legal battle.

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