"The modem federal immigration power, which is commonly known as the "plenary power doctrine," is defined by two features. First, Congress's authority to regulate immigration derives not from any constitutionally enumerated power, but is rather "an incident of sovereignty belonging to the government of the United States." Second, federal laws or enforcement actions that bear on a non-citizen's right to be present within the country are buffered against judicially enforceable constitutional constraints. The extent to which governmental authority is constitutionally constrained is thus contingent on the citizenship status of the person who is subject to that authority, rather than (as would normally be the case) the subject-matter or purpose of the regulation involved. This is true even when the constitutional protection at issue-be it the First Amendment or the Due Process and Equal Protection Clauses-makes no distinction between "persons" and "citizens." Indeed, even as Justice Frankfurter upheld Juan Galvan's deportation, he was struck by "a sense of harsh incongruity" between the principle that "the Due Process Clause[normally] qualifies the scope of [Congress's] political discretion" and the deportation of a long-term resident alien who was innocent of any wrong-doing. Ever since the Supreme Court first adopted the plenary power doctrine in the 1889 Chinese Exclusion Case, so it has justified the "constitutional exceptionalism" " of American immigration law with reference to the purportedly intricate connection between the admission and removal of foreigners and "basic aspects of national sovereignty, more particularly our foreign relations and the national security.,""