Why did McDonald v. City of Chicago leave questions about noncitizens’ firearm rights unresolved?

In McDonald v. City of Chicago (2010), the U.S. Supreme Court held that the Second Amendment right to possess a handgun in the home for self-defense applies to state and local governments through the Fourteenth Amendment’s due process clause.12

However, the decision left the rights of noncitizens unresolved for two primary reasons:

• Case Specifics: The case did not involve a claim brought by a noncitizen, leading Justice Clarence Thomas to explicitly state in his concurring opinion that he expressed no view on the extent to which states may regulate firearm possession by noncitizens.2
• Legal Interpretation: Justice Thomas argued that the Second Amendment should be incorporated through the Fourteenth Amendment’s "privileges or immunities" clause, which he interpreted as recognizing only the rights of "citizens," rather than the broader due process clause that refers to "persons".2

Consequently, the McDonald ruling did not establish whether noncitizens are protected under the Second Amendment, leaving this and other issues—such as the constitutionality of various gun-control regulations—unsettled at the time.2