A joint status report is expected Monday in Doe v. Mattis, in which the United States and the ACLU are locked in legal battle over the fate of an unnamed U.S.-Saudi dual citizen whom the U.S. alleges to be an enemy combatant captured in Syria. The case presents lots of interesting legal issues, many of which Bobby Chesney and Steve Vladeck have covered with their usual insight and attention to detail (available here). The parties are negotiating the possibility of Doe being released into Syria, and thus the case may end soon. It is not publicly known what precisely is at stake in the negotiations, but one possibility is that there is a dispute over whether the government must provide Doe with a passport or other document enabling him to return to the United States if he wishes or to facilitate travel elsewhere in the world. If citizen Doe seeks a U.S. passport, can his own government constitutionally say no?

As important as the freedom of movement is to citizens in our democracy (indeed, to human beings anywhere), there is no explicit textual reference to it in the U.S. Constitution. The Articles of Confederation contained a right to “free ingress and regress,” but this was removed from the final draft of the Constitution without any recorded debate. Nevertheless, courts have routinely protected this right. The strength of this protection is contingent on where the traveler happens to be going.

Domestic—i.e. interstate—travel enjoys the protection of a fundamental right, and the courts strictly scrutinize any attempt by the state to restrict it. But as I note in a book on the subject, no one seems to be able or willing to pinpoint the constitutional source that provides this protection, ascribed over time to various clauses and structural features of the Constitution. When it comes to international travel, the legal protection is less generous, with courts essentially adopting a procedural due process stance on international travel restrictions with the usual thumb on the scales for foreign affairs and national security considerations. (I have argued that there is a fundamental right to international travel that should make its restriction subject to strict scrutiny, too, but I’m pretty alone in this view and it is not now the law.)

None of this would matter if the passport had not evolved over time into what amounts to a license to travel abroad. As such, the constitutional question of access to one often reduces to the usual issues of notice, a chance to be heard and the timing of state action. An additional wrinkle, perhaps unique to passports, comes when the state revokes or cancels a passport when the citizen is already abroad. Edward Everett Hale’s great story “The Man Without a Country” notwithstanding, courts have repeatedly denied the government any power to banish its citizens, even though protection from exile is also not a right found in the text of the Constitution.

So a complete answer may well depend on where John Doe happens to be if he applies for a passport and what he seeks to do with it. Assuming the U.S. government wishes to turn him down, such a denial is on the weakest ground if Doe is seeking to return to the United States. That may be too close to exile, since 8 U.S.C. 1185(b) makes it unlawful “for any citizen of the United States to depart from or enter, or attempt to depart from or enter, the United States unless he bears a valid United States passport.” Assessing a few Cold War-era cases helps to frame the issues that Judge Tanya Chutkan, presiding in the Doe case, might have to consider.

There was a time when passport-less reentry was not only unlawful but also criminal. Denied a passport to travel to Havana in the early 1960s, journalist William Worthy traveled there anyway. Upon arrival in Miami after leaving Cuba, he was indicted for violating this provision (which, at the time, carried a penalty of $5,000 and/or five years’ imprisonment). The initial denial was upheld in Worthy v. Herter by the D.C. Circuit, which had little problem affirming the state’s power to restrict travel out of the country. But in Worthy v. United States, an opinion that has never been distinguished or even subject to judicial doubt, the Fifth Circuit held that “it is inherent in the concept of citizenship that the citizen, when absent from the country to which he owes allegiance, has a right to return, again to set foot on its soil.” The state could not constitutionally require him “to choose between banishment or expatriation on the one hand or crossing the border on the other hand, being faced with criminal punishment and the loss of some of the rights and privileges of citizenship as a felon.” Ironically, the United States has full authority to drag Doe home in an earnest effort to lock him up, but it cannot lock him out.

On the other hand, if Doe is seeking the passport to travel elsewhere or simply to keep his options open, the government is on stronger ground. Philip Agee was a rogue CIA agent who exposed the identities of roughly 250 intelligence officers and assets. (Agee attributed his disillusionment in part to feelings of guilt at his complicity with CIA-backed torture.) The United States revoked his passport with the singular intention of forcing him back home, where, as the solicitor general told the Supreme Court during oral argument in Haig v. Agee, “He would not get out again.” (Contra Worthy’s case, there was no option for criminal prosecution; Agee’s case led to the Intelligence Identities Protection Act of 1982, a statute with which Scooter Libby has a nodding acquaintance.) Writing for himself and six other justices, Chief Justice Warren Burger held that “when there is a substantial likelihood of ‘serious damage’ to national security or foreign policy as a result of a passport holder’s activities in foreign countries, the Government may take action to ensure that the holder may not exploit the sponsorship of his travels by the United States.”

The Court held that Agee’s right to due process would be satisfied by a post-revocation hearing if he were willing to come home to have one. Agee also asserted First Amendment interests, relying on Supreme Court precedents (such as Kent v. Dulles and Aptheker v. Secretary of State) that held that travel restrictions could implicate protected freedoms of speech, religion and assembly. These the court easily distinguished, since it was Agee’s conduct that was damaging national security (and that led to the government revocation), not his beliefs or associations. Even if the content of his speech was implicated, this looked too much like the court’s favorite example in such contexts: “publication of the sailing dates of transports or the number and location of troops” to escape restriction. Keeping in mind William Worthy’s travels, there is irony here, too; Agee was not overly keen to travel back to the United States. Agee died in Havana.

Since Doe is reported to be a dual citizen of both the United States and Saudi Arabia, the question of statelessness is not squarely presented here (and there is no evidence that the U.S. wishes to take away his citizenship). But citizenship-stripping is also a tool that the U.S. and other governments appear to value and have struggled to acquire with varying degrees of success. The United States negotiated the renunciation of Yaser Hamdi’s citizenship in exchange for his release, an effort to avoid the due process hearing the Supreme Court required in Hamdi v. Rumsfeld. This negotiation was necessary because the Supreme Court has repeatedly and conclusively ruled (as it did in 1958 in Trop v. Dulles) that involuntary expatriation “is not a weapon that the Government may use to express its displeasure at a citizen’s conduct, however reprehensible that conduct may be.” The United Kingdom, on the other hand, has asserted the statutory power to strip naturalized British citizens who hold, or may have only the reasonable possibility of acquiring, citizenship elsewhere.

There is much to criticize in “the evil of statelessness,” as the U.K. Supreme Court described it in Secretary of State for the Home Department v. Al-Jedda. And few considered involuntary expatriation worthy of any support when it was a power mostly associated with repressive regimes keen to exile dissidents such as Alexander Solzhenitsyn, welcomed to the United States after his banishment in 1974 from the Soviet Union. But passport denials (like terrorist watch lists) raise similar issues that go to the heart of what it means to be a citizen seeking freedom of movement against the bureaucratic mechanics of international travel restrictions created in the 20th century and perfected in digital form in the 21st.