WASHINGTON − After theSupreme Courtin 2022 made itharder to restrictwho can arm themselves in public, some states took a different approach. Five Democrat-led, mostly densely populous states passed laws that prohibit bringing a handgun onto someone else's property without that person's express consent. Now the Trump administration wants theSupreme Courtto declare that such rules in Hawaii, California, New York, Maryland and New Jersey violate the Constitution. "The United States has a substantial interest in the preservation of the right to keep and bear arms and in the proper interpretation of the Second Amendment," Solicitor General John Sauerwrotein explaining why the Department of Justice wants the high court to weigh in. That's not the only example of how the change in administrations is affecting litigation over gun regulations. In a move alarming to groups working to prevent gun violence, the DOJ declined to continue to defend a federal law setting 21 as the minimum age to own a handgun after an appeals court ruled the restriction unconstitutional. "For the government to step back and say, `Hey, here's a major piece of federal firearms legislation that was passed by Congress; we're just not going to bother to defend it any longer,' that's a really, really significant thing," said Esther Sanchez-Gomez, litigation director for the Giffords Law Center. The DOJ has alsotold the Supreme Courtthat the federal government no longer opposes all aspects of a Missouri law –blocked by lower courtsafter the Biden administration and others challenged it – that would penalize state police for enforcing federal gun control laws. "This is the first time we've seen a Justice Department really actively fight for the Second Amendment rights of all Americans," said Hannah Hill, vice president of the National Foundation for Gun Rights. Hill said it's taken the administration longer than she'd hoped to take a stand and her group is eager for PresidentDonald Trumpto repeal federal regulations − including rules on untraceable "ghost guns" that the Supreme Courtupheldin March. "But you're seeing a slow pivot of a massive ship back toward the Constitution," she said. "And I'm extremely encouraged by the trajectory." During a 2024 campaign stop to address thousands of members of the National Rifle Association in Pennsylvania, Trumppromisedthat "no one will lay a finger on your firearms" if voters put him back in the White House. "Your Second Amendment will always be safe with me as your president,"Trump said. Soon after taking office, Trump signed anexecutive orderdirecting a review of Biden-era firearm policies and of the positions the government has taken in gun-related litigation. Legal challenges to firearm rulesspikedafter the court created a new test for gun laws in its 2022 decision striking down a New York law that required stateresidents to have "proper cause" to carry a handgun. The court said gun rules must be similar to a historical regulation on weapons to pass constitutional muster. As the administration was changing hands in January, the New Orleans-based5thU.S. Circuit Court of Appealssaid a decades-old federal law banning handgun purchases by 18- to 20-year-olds fails that test. "The history of firearm use, particularly in connection with militia service, contradicts the premise that eighteen-to-twenty-year-olds are not covered by the plain text of the Second Amendment," U.S. Circuit Judge Edith Joneswrote for the court. In July, the DOJ told a lower court that the government is not going to appeal that decision to the Supreme Court. But the high court may still take up the issue. More:Supreme Court rules Mexico can't sue US gunmakers over cartel violence In June, the Richmond-based 4thU.S. Circuit Court of Appeals reached the opposite conclusion as the 5thCircuit, ruling against a similar challenge. "From English common law to America's founding and beyond, our regulatory tradition has permitted restrictions on the sale of firearms to individuals under the age of 21," U.S. Circuit Judge J. Harvie Wilkinson IIIwrote for the court. The four 18- to 20-year-olds challenging the age restriction haveappealedthat decision to the Supreme Court. The DOJ has not yet filed its response. More:Supreme Court sides with Biden and upholds regulations of ghost guns to make them traceable In its brief supporting a challenge to Hawaii's law prohibiting the carrying of handguns onto someone else's property without their consent, the government said that the rule "effectively nullifies" the general right to carry a gun in public that the court upheld in 2022. "Someone carrying a firearm for self-defense cannot run errands without fear of criminal sanctions," Sauer told the court. Sanchez-Gomez, the litigation director for the Giffords Law Center, said property owners have always had the ability to restrict weapons. But Hawaii's law makes the default that handguns aren't allowed unless there's express permission, rather than that they are allowed unless they're expressly prohibited. When the court limited states' control over who could publicly carry guns, she said, the focus turned to where in public they could bring them. Alex McCourt, an assistant professor with the Johns Hopkins Center for Gun Violence Solutions, said the Supreme Court could take up the case not so much because the Trump administration wants them to but because one appeals court upheld Hawaii's rule while a different appeals court rejected New York's. "The fact that we have these differing opinions across the country probably weighs even heavier in the Supreme Court's mind," he said. Still, McCourt said, it's relatively rare for the high court to weigh in on gun laws. "They often say no," he said. In June, the justicesdeclinedto hear a challenge to Maryland's ban on assault-style weapons, although Justice Brett Kavanaugh said he expects his colleagues "will address the AR-15 issue soon, in the next term or two." Days later, the Justice Department urged the Chicago-based 7thU.S. Circuit Court of Appeals to strike down a similar law in Illinois. "Because the Act is a total ban on a category of firearms that are in common use by law-abiding citizens for lawful reasons, it is flatly unconstitutional," lawyers for the DOJ wrote in alegal briefsupporting the challenge. The Firearms Policy Coalition, one of the groups fighting Illinois' law, called the DOJ's filing a critical step toward Trump fulfilling his promise to defend the Second Amendment. "We hope Solicitor General Sauer will stand with us on this issue at the Supreme Court," coalition president Brandon Combs said in astatement, "when this case inevitably heads up." This article originally appeared on USA TODAY:Trump wants Supreme Court to crack down on gun rules