How have landmark Supreme Court cases shaped constitutional protections for non-citizens?

1. Historical exclusion then constitutional reversal: Dred Scott to Wong Kim Ark

Early Supreme Court decisions treated certain groups as outside constitutional protection, most infamously Dred Scott’s holding that Black people could not be U.S. citizens, a result overturned by the post‑Civil War Amendments ^[2]. By the end of the 19th century the Court recognized birthright citizenship under the Fourteenth Amendment in U.S. v. Wong Kim Ark, anchoring a constitutional floor for those born here regardless of parental nationality ^[3].

2. Treating non‑citizens as “persons”: due process and equal protection doctrine

The modern premise that non‑citizens present in the United States enjoy core constitutional protections—most importantly the Fifth Amendment’s due process guarantee and, where relevant, the Fourteenth Amendment’s equal protection component—was cemented across several opinions asserting that "persons" within the jurisdiction cannot be deprived of life, liberty, or property without due process ^{[1] [5]}. The Court’s reasoning in cases like Plyler v. Doe extended equal‑protection scrutiny to undocumented children denied public education, emphasizing that presence in the territory triggers constitutional safeguards ^[5].

3. The plenary‑power exception and immigration’s special status

Despite those protections, the Court has long recognized that immigration sits at the intersection of federal political power and national sovereignty, a posture that often grants Congress and the Executive broad authority—what scholars call the “plenary power” doctrine—over admission, exclusion, and removal ^{[6] [3]}. Cases such as Fong Yue Ting upheld congressional authority to expel aliens even as dissents warned that resident aliens merited due‑process protection, demonstrating the Court’s willingness to defer to political branches in immigration policymaking ^[6].

4. Procedural protections: habeas, detention, and the battlefield cases

The Supreme Court has repeatedly been asked to reconcile national‑security exigencies with individual liberty. Litigation over detainees—highlighted by Rasul and Boumediene—forced the Court to consider whether non‑citizens, including enemy combatants, can seek habeas corpus in federal courts, with decisions recognizing limited access to judicial review even in extraordinary contexts ^[4]. Those holdings illustrate that constitutional safeguards can reach into national‑security settings, though the Court has also allowed substantial leeway for the political branches.

5. Limits and distinctions: status, location, and statutory frameworks

The Court’s protection of non‑citizens is not unconditional; it varies by status (e.g., lawful resident, visitor, undocumented), location (interior versus at the border or at sea), and the procedural posture (civil removal versus criminal prosecution). Precedent shows differences in the scope of rights—detention and deportation proceedings are civil and historically afforded fewer procedural protections than criminal cases—while statutes and congressional prerogatives shape outcomes that the Court will often bless absent clear constitutional violations ^{[3] [7]}.

6. Recent iterations and unresolved questions

More recent decisions and pending controversies continue to refine the map: the Court has corrected sex‑based disparities in citizenship transmission and reviewed statutory vagueness in immigration grounds (e.g., Morales‑Santana, Nguyen, Sessions v. Dimaya), showing a willingness to apply equal‑protection and due‑process doctrine to immigration rules ^{[7] [8]}. Simultaneously, litigation over practices like third‑country removals and limits on habeas review indicates that core questions—how far constitutional protections extend to non‑citizens at different locations and under different procedural regimes—remain contested and fact‑driven ^{[9] [4]}.