The legal meaning of the Second Amendment changed significantly, as a result of the lawsuit District of Columbia v. Heller. It started when a security guard in Washington, D.C. challenged the district's strict gun control laws, which essentially prevented him from keeping a firearm in his home for self-defense [source: Duggan].
The lawsuit eventually reached the U.S. Supreme Court, whose 2008 ruling was the first since the Miller case in 1939 to actually interpret what the Second Amendment meant. The court decided that the Second Amendment gave an individual the right to possess a gun for traditionally lawful uses, in particular self-defense. In doing so, the Supreme Court invalidated two parts of the district's law: the ban against handgun possession, and another provision that compelled those who owned weapons that predated the law to either disassemble them or use trigger locks. It found that those rules violated gun owners' rights, because they hindered self-defense [source: LOC].
In the majority opinion, the late Justice Antonin Scalia wrote that the amendment's prefatory clause — the part that talks about "a well regulated militia" — didn't limit the operative clause, which delineated a "right of the people to keep and bear arms" similar to other amendments that used the phrase.
But at the same time, Scalia also noted that the right to bear arms wasn't completely without limits. "Nothing in our opinion should be taken to cast doubt on longstanding prohibitions on the possession of firearms by felons and the mentally ill, or laws forbidding the carrying of firearms in sensitive places such as schools and government buildings, or laws imposing conditions and qualifications on the commercial sale of arms," he wrote [source: Cornell].
A subsequent 2010 Supreme Court decision, McDonald v. City of Chicago, found that the rights recognized in Heller also applied to states and local governments [source: LOC].
But while both of these rulings established that individuals have the right to arm themselves for self-defense, neither cleared up the stickier question of whether the Second Amendment entitled them to carry weapons for protection outside their homes. Federal appellate and state high courts had taken different positions on that issue.
The Supreme Court had declined, in a 2017 case called Peruta v. California, to rule on the issue. But justices Clarence Thomas and Neil Gorsuch indicated that they believed the Second Amendment extended to carrying weapons for protection in public places as well. The justices wrote, in a dissent from the denial of certiorari for the case, that they found it "extremely improbable that the Framers understood the Second Amendment to protect little more than carrying a gun from the bedroom to the kitchen." To believe that, the justices wrote, would be to conflate "bearing" arms with "keeping" them [source: Volokh].