I used the FDR detention of Japanese descendants as my example for a reason.
The fact that it was not a law (but could have been) is not important. The example served its purpose all the same.
IF such a "law" got passed tomorrow (substitute Arab for Japanese): it would be (in my estimation) pretty clearly UnConstitutional. Would it be any less so just because no Court had yet made that pronouncement?
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I see your premise, I am not disagreeing with you in principle, as CJ Taney, when he was circuit riding, struck down Lincoln's suspension of HC.
The Patriot Act is a good example also, detaining suspected terrorists without the benefit of HC.
Although the "presumption" is there of the Constitutionality of a law, I know where you are coming from, and it is a valid argument.