"National security" does not at all relate to "continued existence of the U.S. government". The government will exist as long as the survivors allow it to.
On the contrary, it has to do with, literally, the security of the nation itself. Nothing more or less.
We wouldn't wait to establish martial law if necessary during invasion until the government were about to fall, after all. The Confederate invasion of Pennsylvania that was stopped at Gettysburg is about as "national security" as it got for the U.S., but that never directly threatened the U.S. government itself.
...the security of the nation itself. Nothing more or less.
"Nothing more or less" sounds so precise, but "the security of the nation" is (like "national security") so vague as to be virtually meaningless without elaboration. "National security" is often abused to mean pretty much whatever the speaker wants it to mean. But it has always been very much about the continued existence and authority of the government.
"National security" as a concept and term didn't exist in the Civil War, but the main threat to "national security" at the time was the attempted secession of several states, which, had it succeeded, would have dramatically altered the power, authority, and nature of the US government.
> which, had it succeeded, would have dramatically altered the power, authority, and nature of the US government.
But it would not have altered the existence of that government. It would, on the other hand, have threatened the republican form of government which the Constitution requires the government to provide for its citizens in Article IV.
Of course, I was speaking of actual invasion anyways, not mere secession.
On the contrary, it has to do with, literally, the security of the nation itself. Nothing more or less.
We wouldn't wait to establish martial law if necessary during invasion until the government were about to fall, after all. The Confederate invasion of Pennsylvania that was stopped at Gettysburg is about as "national security" as it got for the U.S., but that never directly threatened the U.S. government itself.