He could probably deport them if he chose to. Since the act was mentioned, I wanted to give an interesting tidbit about the act. in 1948, the Supreme Court held that the only determinations a court can make regarding the Alien Enemy Act is whether the factual basis for President's proclamations are truthful, i.e. if President activated his powers because of war, then the court can review whether there is war. Ludecke v. Watkins, 335 U.S. 160, 68 S. Ct. 1429, 92 L. Ed. 1881 (1948). This year, the Supreme Court partly overruled this. In Trump v. J. G. G., 604 U. S. ____ (2025), the court instead claimed that the courts can only review whether the act itself is constitutional (in 1948 Supreme Court determined that it obviously was) and whether the alien fits within the President's determinations - but, not the determinations themselves.
I found that pretty interesting.