The Supreme Court on Tuesday appeared to lean toward upholding the Biden administration’s regulations of so-called ghost guns.  Sold as do-it-yourself kits, the devices enable a user to assemble a fully functional firearm in a matter of minutes.   The Biden administration has raised alarm about ghost guns’ exploding popularity and difficulty in tracing them. Law enforcement seized roughly 1,600 ghost guns used in crimes in 2017, and the figure quickly grew to more than 19,000 in 2021, the Justice Department said.  Two years ago, President Biden cracked down on the devices by having his Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) regulate them like any other firearm.   The regulation mandates the devices boast serial numbers, sellers be licensed and buyers complete background checks, among other requirements.  The regulation faces a challenge from five gun manufacturers and distributors, two gun rights groups and two individuals, who contend that ghost guns can’t be categorized as a “firearm” as defined under federal law.  “ATF has now exceeded its authority by operating outside of the bounds set by Congress,” Peter Patterson, who represented the challengers, told the justices.  A majority of the court, including the three liberal justices, appeared sympathetic toward the government’s assertion that it wasn’t overstepping its authority.  “The agency just taking over what is really Congress's business — is that a storyline that the respondents here can tell about this regulation?” asked Justice Elena Kagan.  “No, I don't think there is any tenable way to characterize this regulation as an attempt to change the meaning of the statute to confront a new problem,” responded U.S. Solicitor General Elizabeth Prelogar.  But not all the justices seemed convinced.  “You make a lot of the fact that this has been regulated for half a century, but it wasn't regulated in this way for a half century,” conservative Justice Clarence Thomas pressed the government. The Gun Control Act of 1968 defines firearms to include weapons “designed to or may readily be converted to expel a projectile by the action of an explosive” and the “frame or receiver” of such weapons.   Much of Tuesday’s questioning revolved around whether a ghost gun, which is generally sold as a parts kit, is complete enough to meet the criteria.  Justice Samuel Alito at one point held up a pen and a yellow notepad with nothing written. “Alright, is this a grocery list?” he asked Prelogar.  He then went on to another hypothetical: “I put out on a counter, some eggs, some chopped-up ham, some chopped-up pepper and onions. Is that a Western omelet?”  Prelogar responded no to both.  “Would your answer change if you ordered it from HelloFresh and you got a kit?” Justice Amy Coney Barrett followed up.  Prelogar said it did change the analysis.  “If you bought from Trader Joe's some omelet-making kit that had all of the ingredients to make the omelet, and maybe included whatever you would need to start the fire in order to cook the omelet ... we would recognize that for what it is. And it doesn't stretch plain English to say I bought omelets at the store,” she said.  On two previous occasions, the Supreme Court has intervened on its emergency docket to revive the Biden administration’s ghost gun regulation.   The high court did so the first time by a vote of 5-4, with Barrett and Chief Justice John Roberts joining the court’s three liberals in the majority. There were no noted dissents the second time, though that instance centered on whether lower courts were countermanding the justices’ authority.  Justice Brett Kavanaugh, another conservative whose ideology is regarded as being near the center of the court, had voted against the Biden administration at the emergency stage.  On Tuesday, Kavanaugh explained his reasoning for the first time publicly. He told Prelogar the government’s expanded interpretation “has force,” but he was concerned that it could lead to criminal penalties for people who didn’t realize gun regulations reached that far.  “What about the seller, for example, who is truly not aware that they are violating the law and gets criminally charged? What assurances can you give?” Kavanaugh asked.  Prelogar noted that most cases would require showing that the seller was willfully violating the law.  The dispute is the second Supreme Court case in as many terms implicating whether the executive branch has overstepped in regulating firearms.  Last term, the high court along its 6-3 ideological lines invalidated Trump-era ATF regulations banning bump stocks, which convert semiautomatic weapons to ones capable of firing hundreds of rounds per minute.