The precedent arising from the Millard Gillars treason prosecution is Gillars v. United States, 182 F.2d 962 (D.C. Cir. 1950). There were numerous issues raised on appeal but portion of the opinion regarding what counts as treason is as follows:
The theory of this contention is that treason may not be committed by
words, that all vocal utterances are, by reason of their nature and
regardless of all else, an exercise of freedom of thought, which may
not be prohibited by condemning the expression of thought by words.
Expression of thought or opinion about the Government or criticism of
it is not treason. The oppressive use of the power of government to
destroy political enemies by accusing them of crime underlay the
determination of the framers of our Constitution to limit treason to
acts, and to such acts only as come within the definition which is
embedded in the Constitution itself. In addition, the First Amendment
bars enlarging treason to include the mere expression of views,
opinion or criticism. There is more to the crime than this.
In Cramer v. United States, supra, 325 U.S. at page 29, 65 S.Ct.at
page 932, the Supreme Court has said:
‘ * * * the crime of treason consists of two elements: adherence to
the enemy; and rendering him aid and comfort. A citizen intellectually
or emotionally may favor the enemy and harbor sympathies or
convictions disloyal to this country's policy or interest, but so long
as he commits no act of aid and comfort to the enemy, there is no
treason. On the other hand, a citizen may take actions which do aid
and comfort the enemy- making a speech critical of the government or
opposing its measures, profiteering, striking in defense plants or
essential work, and the hundred other things which impair our cohesion
and diminish our strength- but if there is no adherence to the enemy
in this, if there is no intent to betray, there is no treason.’
There is no question in our mind that words may be an integral part of
the commission of the crime if the elements which constitute treason
are present; that is, if there is adherence to and the giving of aid
and comfort to the enemy by an overt act proved by two witnesses, with
intention to betray, though the overt act be committed through speech.
A similar question has been similarly decided in Chandler v. United
States, 1 Cir., 1948, 171 F.2d 921, certiorari denied, 1948, 336 U.S.
918, 69 S.Ct. 640, 93 L.Ed. 1081. See, also, United States v. Best,
D.C. Mass. 1948, 76 F.Supp. 857; Rex v. Joyce, 173 L.T.R. 377,
Affirmed sub nom, Joyce v. Director of Public Prosecutions, (1946)
A.C. 347; Charge to Grand Jury- Treason, C.C.S.D. Ohio 1861, 30
Fed.Cas.at pp. 1036, 1037, No. 18,272 (communication of intelligence
to the enemy); Charge to Grand Jury- Treason, C.C.S.D.N.Y. 1861, 30
Fed.Cas.at pages 1034, 1035, No. 18,271 (advising, inciting or
persuading others to give aid and comfort to the enemy); and Cramer v.
United States, supra, 325 U.S.AT page 29, 65 S.Ct. 918. While the
crime is not committed by mere expressions of opinion or criticism,
words spoken as part of a program of propaganda warefare, in the
course of employment by the enemy in its conduct of war against the
United States, to which the accused owes allegiance, may be an
integral part of the crime. There is evidence in this case of a course
of conduct on behalf of the enemy in the prosecution of its war
against the United States. The use of speech to this end, as the
evidence permitted the jury to believe, made acts of words. The First
Amendment does not protect one from accountability for words as such.
It depends upon their use. It protects the free expression of thought
and believe as a part of the liberty of the individual as a human
personality. But words which reasonably viewed constitute acts in
furtherance of a program of an enemy to which the speaker adheres and
to which he gives aid with intent to betray his own country, are not
rid of criminal character merely because they are words.
Gillars v. U.S., 182 F.2d 962, 970–71 (D.C. Cir. 1950).
A roughly contemporaneous case involving similar facts that relied on Gillars as precedent was Best v. United States, 184 F.2d 131 (1st Cir. 1950).
It was also referenced regarding what constituted sufficient duress to excuse a violation of the code of military justice seven years later. U.S. v. Olson, 1957 WL 4621 (Court of Military Appeals 1957). The Courts in Gillars and Olson discounted duress defenses because the acts constituting the alleged duress were too feeble.
The most recent case citing it for this point of law was in a case seeking to invalidate veteran's benefits for aiding an enemy during the Korean War.
The findings of fact and the conclusions of law made by the Veterans
Administration are fully supported by substantial evidence. It is well
settled that aid and assistance to the enemy may be extended in the
form of verbal utterances alone, as was the case in this instance.
Cramer v. United States, 325 U.S. 1, 29, 65 S.Ct. 918, 89 L.Ed. 1441;
United States v. Burgman, D.C., 87 F.Supp. 568, 571; 88 U.S.App.D.C.
184, 188 F.2d 637; Gillars v. United States, 87 U.S.App.D.C. 16, 25,
182 F.2d 962; Chandler v. United States, 1 Cir., 171 F.2d 921, 938;
Iva Ikuko Toguri D'Aquino v. United States, 9 Cir., 192 F.2d 338, 366.
Thompson v. Whittier, 185 F. Supp. 306, 314 (D.D.C 1960)
In my view, it is rather doubtful that the precedent created by that conviction would still be good law on the facts presented. Constitutional First Amendment law in the U.S. has evolved a lot since 1950, and the fact that this case has not been relied upon by other courts since 1960 suggests that this may be a case that has been implicitly repealed or narrowed, even though no specific court has addressed the validity of this particular precedent.
This was also a quite fact specific ruling. The introductory portion of the Gillars opinion states that:
Appellant was convicted of treason in a jury trial in the United
States District Court for the District of Columbia. Treason alone of
crimes is defined in the Constitution, as follows:
"Treason against the United States, shall consist only in levying War
against them, or in adhering to their Enemies, giving them Aid and
Comfort. * * *" U.S. Const. Art. III, § 3.1
The First Congress, in 1790, provided by statute,
"* * * That if any person or persons, owing allegiance to the United
States of America, shall levy war against them, or shall adhere to
their enemies, giving them aid and comfort within the United States or
elsewhere, and shall be thereof convicted, on confession in open
court, or on the testimony of two witnesses to the same overt act of
the treason whereof he or they shall stand indicted, such person or
persons shall be adjudged guilty of treason against the United States,
The indictment alleges that appellant was born in Maine, was a citizen
of and owed allegiance to the United States, that within the German
Reich, after December 11, 1941, to and including May 8, 1945, in
violation of her duty of allegiance she knowingly and intentionally
adhered to the enemies of the United States, to wit, the Government of
the German Reich, its agents, instrumentalities, representatives and
subjects with which the United States was at war, and gave to said
enemies aid and comfort within the United States and elsewhere, by
participating in the psychological warfare of the German Government
against the United States. This participation is alleged to have
consisted of radio broadcasts and the making of phonographic
recordings with the intent that they would be used in broadcasts to
the United States and to American Expeditionary Forces in French North
Africa, Italy, France and England. The indictment charges the
commission of ten overt acts, each of which is described, and,
finally, that following commission of the offense the District of
Columbia was the first Federal Judicial District into which appellant
Eight of the ten alleged overt acts were submitted to the jury. A
verdict of guilty was returned, based on the commission of overt act
No. 10, which is set forth in the indictment as follows:
"10. That on a day between January 1, 1944 and June 6, 1944, the exact
date being to the Grand Jurors unknown, said defendant, at Berlin,
Germany, did speak into a microphone in a recording studio of the
German Radio Broadcasting Company, and thereby did participate in a
phonographic recording and cause to be phonographically recorded a
radio drama entitled "Vision of Invasion," said defendant then and
there well knowing that said recorded radio drama was to be
subsequently broadcast by the German Radio Broadcasting Company to the
United States and to its citizens and soldiers at home and abroad as
an element of German propaganda and an instrument of psychological
To the extent that it is still good law, a formal oath of allegiance to Hitler and the Third Reich which she swore while a declared war against Germany was pending was an important distinguishing fact from most other cases. The oath of allegiance established beyond a reasonable doubt, the element of adherence to the enemy. See "TREASON: True to the Red, White & Blue", Time (March 7, 1949) (cited in the Wikipedia article in the original post).
Other answers correctly note that in the context of the constitutional definition of treason, "enemy" is narrowly defined to mean a country (or perhaps an organization) with which the United States is at war, and not merely a domestic political faction or a country with whom the U.S. is not on good terms and sees as a rival and adversary outside the context of an actual war.
This case is also not an application of the "fire" in a crowded theater theory of a First Amendment exception, which among other things, involving a knowing falsehood used to incite panic, and not a truthful one. This is an entirely different theory. The veracity of her propaganda was not an issue in her case.
The theory in her case was basically a "verbal acts" theory, similar to the theory that saying "I accept" in a contract negotiation is a verbal act and not just an expressive statement of a viewpoint protected under the First Amendment.
It is also worth noting that ten charges were filed, two were dismissed prior to trial by the court, and she was convicted of only one of the remaining eight counts. This suggests that the jury found that most of the overt acts she allegedly committed did not rise to the level of treason.