I was just looking over the Heller opinion, and came across the debate between Justices Scalia and Stevens about U.S. v. Cruikshank, 92 U.S. 542 (1876). Here's what Justice Stevens's dissent argues, accurately quoting both Cruikshank and the majority (citations omitted):
In United States v. Cruikshank, the Court sustained a challenge to respondents' convictions under the Enforcement Act of 1870 for conspiring to deprive any individual of "'any right or privilege granted or secured to him by the constitution or laws of the United States.'" The Court wrote, as to counts 2 and 10 of respondents' indictment:
"The right there specified is that of 'bearing arms for a lawful purpose.' This is not a right granted by the Constitution. Neither is it in any manner dependent on that instrument for its existence. The second amendment declares that it shall not be infringed; but this, as has been seen, means no more than that it shall not be infringed by Congress. This is one of the amendments that has no other effect than to restrict the powers of the national government."
The majority's assertion that the Court in Cruikshank "described the right protected by the Second Amendment as '"bearing arms for a lawful purpose,"'" is not accurate. The Cruikshank Court explained that the defective indictment contained such language, but the Court did not itself describe the right, or endorse the indictment's description of the right.
This is mighty odd (as the Heller majority stressed, in note 22). Cruikshank says, "The second amendment declares that it shall not be infringed ... by Congress." What is "it"? The only possible referent is "The right there specified," namely "of 'bearing arms for a lawful purpose.'"
Thus, substituting the referent, we see Cruikshank saying that "The second amendment declares that [the right of bearing arms for a lawful purpose] shall not be infringed ... by Congress." So Cruikshank definitely does describe the right protected by the Second Amendment.
Maybe I'm missing something here, but I don't think I am: It seems to me that the dissent just flatly misread Cruikshank, and in an important way -- and didn't correct this despite Justice Scalia's express and accurate response in footnote 22 of the majority.
So this is one reason I tell my students: Never rely on an intermediate source's characterization (or even quotation) of an original source; always read, quote, and cite the original source. (True, sometimes when the intermediate source is authoritative -- for instance, is a majority opinion -- its mischaracterization of an original source may itself create binding law. But the original source still says what the original source always said.)