A gun rights group has sued the Justice Department to overturn this prohibition, which became law as part of the Gun Control Act of 1968, and the case is now in front of U.S. District Judge James Robertson in Washington, D.C.
Narrowly speaking, the Second Amendment Foundation has filed the Hodgkins v. Holder suit on behalf of American citizens who live abroad and would like to buy firearms when they return for a visit (but can't because Form 4473 requires them to list what U.S. state they live in). More broadly, it could restore Americans' right to buy handguns while traveling across state lines as long as they undergo the normal federal background check.
Federal law says that, in general, it is unlawful for a dealer to sell a handgun to "any person who the licensee knows or has reasonable cause to believe does not reside in the state." Rules for buying a rifle or shotgun are a little less strict.
Attorneys for both sides have been arguing over whether the American expats have suffered enough harm to permit them to sue, a legal concept called standing. The Obama administration claims that they haven't, arguing in a brief: "(Plaintiff's) vague allegation of an intention to acquire a firearm on some future visit to the United States does not give rise to a live controversy as required by Article III of the Constitution." In response, the Second Amendment Foundation points out that the expats tried to purchase firearms in the past but were denied permission.
A ruling last Friday by the U.S. Court of Appeals for the District of Columbia could affect how that question is resolved. Two of the judges on the panel said there was no need to change the current rule on standing; the dissent by Judge Janice Brown said it conflicted with Supreme Court precedent: "Our doctrine thereby enables the government to deprive a plaintiff of pre-enforcement standing simply by being silent or deliberately vague about its intentions. Unless declaratory relief is available, prosecutors can act strategically to protect criminal laws or arbitrary enforcement procedures from judicial review. That is essentially what happened here."
For the record, Alan Gura, the attorney who is representing the Second Amendment Foundation, thinks he can win on the standing question one way or another. "In Hodgkins we have enough facts. They tried to buy guns but couldn't. That's more than pre-enforcement standing."
While this may be an intricate legal question that only lawyers might fully appreciate, it offers a glimpse into how the legal system operates in practice. Courts don't always reach -- they're often hesitant to reach -- broad questions about a law's constitutionality. Procedural rules are hugely important.
In this case, for instance, the Obama administration appears to have taken the position that there's no way for anyone to challenge the 1968 Gun Control Act on Second Amendment grounds unless they're arrested for violating it first. Any volunteers?
Declan McCullagh is a senior correspondent for CBSNews.com. He can be reached at email@example.com and can be followed on Twitter as declanm. You can bookmark Declan's Taking Liberties site here, or subscribe to the RSS feed. Before becoming a CBS employee, Declan was chief political correspondent for CNET, a reporter for Time, and Washington bureau chief for Wired.