While the government may have discretion to act outside of the courts, its officers often will not, allowing due process to play out in the courts.
One of the key cases in modern Constitutional Law is Korematsu v. United States, where the Supreme Court held that the exclusion of Japanese citizens from large parts of the West Coast was constitutional. (While the case technically did not cover the internment of the Japanese, the exclusion of Japanese from such a large area without any individualized suspicion renders both internment and exclusion to be largely subject to the same analysis that I make here.) This case is normally thought to represent an egregious failure on the part of the Supreme Court to enforce constitutional law.
But things are more complicated than they at first seem. To begin with, the normal argument is that the Supreme Court should have struck down the exclusion and internment as a violation of the Equal Protection Clause. But the Equal Protection Clause does not apply to the federal government. For that reason, the major nonoriginalist critics of Korematsu argue strenuously that the Equal Protection principles are somehow reverse incorporated or otherwise applied to the federal government. That ignores the text and is a mistake. For more of my views on the matter, see here.
The more promising textual basis for holding the exclusion and internment as unconstitutional is that they exceed Congress’s enumerated powers. But this path is not open to the major nonoriginalist critics of Korematsu, since they embraced extremely broad national powers. Thus, those critics are not able to argue that the original basis for protecting civil liberties in the federalist structure of the Constitution is what protected against the Japanese exclusion and internment.
What power allowed either the Congress or the President to exclude and intern Japanese citizens without any substantial evidence that these individuals were dangerous? Congress has the power to declare war, to define and punish offenses against the law of nations, and to make rules for the armed forces. But the original meaning of none of these powers allows for the federal government to exclude or intern an entire race of citizens without substantial evidence of their being dangerous.
Nor does the President’s commander in chief power allow him to do it. Excluding and interning these citizens did not involve the movement of armies in a war zone. The President is commander in chief of the armed forces, not of the nation.
Presumably, Congress would claim that it is exercising its power to take necessary and proper measures to declaring war – to engage in the successful pursuit of the war. But this argument is problematic. Congress cannot simply do whatever it pleases if it believes that this will promote the war effort. It no more has this power than it has the power to do whatever it pleases if it believes that this will influence interstate commerce. The enumerated powers have real limits.
It is true that Congress does have significant power under its necessary and proper authority to conduct a war. Congress can certainly pass a law that prohibits and punishes the actions of enemy spies or saboteurs who come into the country during wartime. But that is clearly distinguishable from the exclusion and internment. The law would prohibit the actual spying or sabotaging. One might possibly – although not certainly – say that Congress could take preventive measures that restricted the actions of people who were suspected with some evidence of engaging in wrongdoing. But that would be as far as one could go. That view would not allow Congress to exercise authority as to all Japanese, nor could Congress use it for mass exclusions and internments.
Of course, this position requires the courts to draw a line under the Necessary and Proper Clause. And therefore the New Deal coalition could never endorse this view. The New Deal ended up supporting the Korematsu decision (6 of the 8 Justices appointed by Roosevelt were in the majority) and the dissenters disapproved the ruling based on a made up constitutional right.