[AndyJackson]

The proper ruling from the court would be not to rule on the issue of machine guns

That is not an issue in controversy in this case and so no Court has jurisdiction to rule on that issue.

[Atlas Sneezed]

That is not an issue in controversy in this case and so no Court has jurisdiction to rule on that issue.

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So the DOJ is wrong to inject it, in an effort to goad SCOTUS into ruling on it.