When I read the text of the amendment, I think that they very much would have considered it to cover everyone.
"No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger;"
Our declaration of independence says that "We hold these truths to be self-evident, that all men are created equal" -- ALL men. Not just American men. I think those two, taken together, imply that the founders would have meant for the 5th amendment to cover American men, Englishmen, Frenchmen, and natives of foreign lands which they had not heard of yet.
1. Assume for the sake of argument that imprisonment of suspected terrorists without trial violates the Fifth Amendment. The question then becomes: What must the government do about the violation --- that is, what is the prisoner's remedy?
A) The canonical remedy for unlawful imprisonment is the writ of habeas corpus [1]. When a court issues "the Great Writ," it orders the prisoner's jailer(s) to bring the prisoner to court and, by implication, to release the prisoner if the court so directs.
B) Article 1 of the Constitution expressly empowers Congress to suspend habeas corpus --- in other words, to strip from courts the authority to order the release of prisoners --- "when in Cases of Rebellion or Invasion the public Safety may require it." [2] Nothing in the Fifth Amendment alters this congressional power of suspension.
C) It might be argued that in enacting the Patriot Act, Congress partially suspended habeas corpus in response to the "Invasion" we call 9/11.
D) The courts try to interpret the various parts of the Constitution to be in harmony with one another if at all possible.
E) So, "properly" interpreted, the Fifth Amendment might not stand in the way of imprisonment without trial in a case covered by a congressional suspension of habeas corpus. (The breadth of this possibility troubles me, incidentally; also, I'm far from a constitutional scholar.)
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2. As to whether the Constitution prohibits killing an enemy combatant in wartime without individualized due process in each case: That'd be a really, really tough sell, not least because if that principle had been followed, the U.S. would not long have survived as an independent state.
"It might be argued that in enacting the Patriot Act, Congress partially suspended habeas corpus in response to the "Invasion" we call 9/11."
Even if someone did argue for that, which you didn't do, they would argue that 9/11 was an "invasion", not an invasion. See how that works?
Also, the perpetrators were from Saudi Arabia mostly, yet Iraq was attacked, talking about how he's an evil man which had fuck all to do with him attacking the US. That's kinda where your whole post falls down like a house of cards. Remember Powell before the UN, with a dry throat and sweating a lot, showing his slides about what might be mobile WMD labs? Heh. No, to anyone not accomplice to it, or suffering from Stockholm Syndrome, this is rather clear. And it's old. Americans have been warning Americans for a century now. The military industrial complex doesn't do this since lately.
As to whether the Constitution prohibits killing an enemy combatant in wartime without individualized due process in each case: That'd be a really, really tough sell
If you simply define "military age males" who died in drone attacks as those, then they're not really enemy combatants, they're "enemy combatants", which raises the same issue as the "invasion" stuff does. Also, simply attacking people and calling it war doesn't make it "wartime". Just saying "it's war!" doesnt make it war.
It can't have been that self-evident that all men were equal when they wrote the Constitution. Indians didn't count and slaves only counted for 3/5 of a person.
"according to their respective Numbers, which shall be determined by adding to the whole Number of free Persons, including those bound to Service for a Term of Years, and excluding Indians not taxed, three fifths of all other Persons."
That specifically states that not all men are equal.
If you want to get an idea of what protections the founders thought should apply to non-Americans outside U.S. soil, you need look no further than see how they handled the American Indians. Hint: they didn't bring Indian chiefs to Philadelphia for trials in American courts.
If you want to be completely literal and pedantic about it, "in the land and naval forces" refers to persons serving in the Army, Navy, and Marines (or their historical equivalents).
Just a note, the declaration of independence is not part of the law in the US. In fact, there is little overlap between the signers of the declaration of independence and the framers of the Constitution.
You can't say with a straight face that the founders thought Constitutional protections should apply to everyone, even people abroad, when they declined to extend any protection to black men living in America. Or Indians. Or women.
Except that you can say it with a straight face. The fact that they had to explicitly call out exceptions for Indians and Blacks means that they felt that they would have otherwise fallen under the general classification of "men".
"No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger;"
Our declaration of independence says that "We hold these truths to be self-evident, that all men are created equal" -- ALL men. Not just American men. I think those two, taken together, imply that the founders would have meant for the 5th amendment to cover American men, Englishmen, Frenchmen, and natives of foreign lands which they had not heard of yet.