From the summary of Overview of the Federal Government’s Power to Exclude Aliens (Sept. 27, 2017 R 44969):
The Supreme Court has determined that inherent principles of sovereignty give Congress “plenary power” to regulate immigration. The core of this power—the part that has proven most impervious to judicial review—is the authority to determine which aliens may enter the country and under what conditions. The Court has determined that the executive branch, by extension, has broad authority to enforce laws concerning alien entry mostly free from judicial oversight. Two principles frame the scope of the political branches’ power to exclude aliens. First, nonresident aliens abroad cannot challenge exclusion decisions because they do not have constitutional or statutory rights with respect to entry. Second, even when the exclusion of a nonresident alien burdens the constitutional rights of a U.S. citizen, the government need only articulate a “facially legitimate and bona fide” justification to prevail against the citizen’s constitutional challenge.
The merits of these so-called “Travel Ban” cases raise significant questions about the extent to which the rights of U.S. citizens limit the executive power to exclude aliens. It seems relatively clear that, under existing jurisprudence, the “facially legitimate and bona fide” standard should govern the Establishment Clause claims against the revised executive order. However, Supreme Court precedent does not clarify whether that standard contains an exception that might permit courts to test the government’s proffered justification for an exclusion by examining the underlying facts in particular circumstances. Nor does Supreme Court precedent resolve whether the standard governs U.S. citizens’ statutory claims against executive exercise of the exclusion power, or even whether such statutory claims are cognizable. The outcome of the Travel Ban cases would likely turn upon these issues, if the Supreme Court were to decide the cases on the merits rather than on a threshold question such as mootness (a key issue in light of a presidential proclamation modifying the entry restrictions at issue in the cases).