Article III, Section 3, Clause 1:
Treason against the United States, shall consist only in levying War against them, or in adhering to their Enemies, giving them Aid and Comfort. No Person shall be convicted of Treason unless on the testimony of two Witnesses to the same overt Act, or on Confession in open court.
Early judicial interpretation of the meaning of treason in terms of levying war was conditioned by the partisan struggles of the early nineteenth century, which involved the treason trials of Aaron Burr and his associates. In Ex parte Bollman, 1 which involved two of Burr's confederates, Chief Justice Marshall, speaking for himself and three other Justices, confined the meaning of levying war to the actual waging of war.
However flagitious may be the crime of conspiring to subvert by force the government of our country, such conspiracy is not treason. To conspire to levy war, and actually to levy war, are distinct offences. The first must be brought into open action by the assemblage of men for a purpose treasonable in itself, or the fact of levying war cannot have been committed. So far has this principle been carried, that . . . it has been determined that the actual enlistment of men to serve against the government does not amount to levying war. Chief Justice Marshall was careful, however, to state that the Court did not mean that no person could be guilty of this crime who had not appeared in arms against the country.
On the contrary, if war be actually levied, that is, if a body of men be actually assembled for the purpose of effecting by force a treasonable purpose, all those who perform any part, however minute, or however remote from the scene of action, and who are actually leagued in the general conspiracy, are to be considered as traitors. But there must be an actual assembling of men, for the treasonable purpose, to constitute a levying of war. 2
On the basis of these considerations and because no part of the crime charged had been committed in the District of Columbia, the Court held that Bollman and Swartwout could not be tried in the District, and ordered their discharge. Marshall continued by saying that
the crime of treason should not be extended by construction to doubtful cases and concluded that no conspiracy for overturning the Government and
no enlisting of men to effect it, would be an actual levying of war. 3
The Burr Trial
Not long afterward, the Chief Justice went to Richmond to preside over the trial of Aaron Burr. His ruling 4 denying a motion to introduce certain collateral evidence bearing on Burr's activities is significant both for rendering the latter's acquittal inevitable and for the qualifications and exceptions made to the Bollman decision. In brief, this ruling held that Burr, who had not been present at the assemblage on Blennerhassett's Island, could be convicted of advising or procuring a levying of war only upon the testimony of two witnesses to his having procured the assemblage. This operation having been covert, such testimony was naturally unobtainable. The net effect of Marshall's pronouncements was to make it extremely difficult to convict one of levying war against the United States short of the conduct of or personal participation in actual hostilities. 5
Aid and Comfort to the Enemy
The Cramer Case
Since Bollman, the few treason cases that have reached the Supreme Court were outgrowths of World War II and have charged adherence to enemies of the United States and the giving of aid and comfort. In the first of these, Cramer v. United States, 6 the issue was whether the
overt act had to be
openly manifest treason or if it was enough if, when supported by the proper evidence, it showed the required treasonable intention. 7 The Court, in a five-to-four opinion by Justice Jackson, in effect took the former view holding that
the two-witness principle interdicted
imputation of incriminating acts to the accused by circumstantial evidence or by the testimony of a single witness, 8 even though the single witness in question was the accused himself.
Every act, movement, deed, and word of the defendant charged to constitute treason must be supported by the testimony of two witnesses, 9 Justice Jackson asserted. Justice Douglas in a dissent, in which Chief Justice Stone and Justices Black and Reed concurred, contended that Cramer's treasonable intention was sufficiently shown by overt acts as attested to by two witnesses each, plus statements made by Cramer on the witness stand.
The Haupt Case
The Supreme Court sustained a conviction of treason, for the first time in its history, in 1947 in Haupt v. United States. 10 Here it was held that although the overt acts relied upon to support the charge of treason – defendant's harboring and sheltering in his home his son who was an enemy spy and saboteur, assisting him in purchasing an automobile, and in obtaining employment in a defense plant – were all acts which a father would naturally perform for a son, this fact did not necessarily relieve them of the treasonable purpose of giving aid and comfort to the enemy. Speaking for the Court, Justice Jackson said:
No matter whether young Haupt's mission was benign or traitorous, known or unknown to the defendant, these acts were aid and comfort to him. In the light of this mission and his instructions, they were more than casually useful; they were aids in steps essential to his design for treason. If proof be added that the defendant knew of his son's instruction, preparation and plans, the purpose to aid and comfort the enemy becomes clear. 11
The Court held that conversation and occurrences long prior to the indictment were admissible evidence on the question of defendant's intent. And more important, it held that the constitutional requirement of two witnesses to the same overt act or confession in open court does not operate to exclude confessions or admissions made out of court, where a legal basis for the conviction has been laid by the testimony of two witnesses of which such confessions or admissions are merely corroborative. This relaxation of restrictions surrounding the definition of treason evoked obvious satisfaction from Justice Douglas, who saw in Haupt a vindication of his position in Cramer. His concurring opinion contains what may be called a restatement of the law of treason and merits quotation at length:
As the Cramer case makes plain, the overt act and the intent with which it is done are separate and distinct elements of the crime. Intent need not be proved by two witnesses but may be inferred from all the circumstances surrounding the overt act. But if two witnesses are not required to prove treasonable intent, two witnesses need not be required to show the treasonable character of the overt act. For proof of treasonable intent in the doing of the overt act necessarily involves proof that the accused committed the overt act with the knowledge or understanding of its treasonable character.
The requirement of an overt act is to make certain a treasonable project has moved from the realm of thought into the realm of action. That requirement is undeniably met in the present case, as it was in the case of Cramer.
The Cramer case departed from those rules when it held that ‘The two-witness principle is to interdict imputation of incriminating acts to the accused by circumstantial evidence or by the testimony of a single witness.'  12
The Kawakita Case
Kawakita v. United States 13 was decided on June 2, 1952. The facts are sufficiently stated in the following headnote:
At petitioner's trial for treason, it appeared that originally he was a native-born citizen of the United States and also a national of Japan by reason of Japanese parentage and law. While a minor, he took the oath of allegiance to the United States; went to Japan for a visit on an American passport; and was prevented by the outbreak of war from returning to this country. During the war, he reached his majority in Japan; changed his registration from American to Japanese, showed sympathy with Japan and hostility to the United States; served as a civilian employee of a private corporation producing war materials for Japan; and brutally abused American prisoners of war who were forced to work there. After Japan's surrender, he registered as an American citizen; swore that he was an American citizen and had not done various acts amounting to expatriation; and returned to this country on an American passport. The question whether, on this record, Kawakita had intended to renounce American citizenship, said the Court, in sustaining conviction, was peculiarly one for the jury and their verdict that he had not so intended was based on sufficient evidence. An American citizen, it continued, owes allegiance to the United States wherever he may reside, and dual nationality does not alter the situation. 14
Doubtful State of the Law of Treason Today
The vacillation of Chief Justice Marshall between the Bollman 15 and Burr 16 cases and the vacillation of the Court in the Cramer 17 and Haupt 18 cases leave the law of treason in a somewhat doubtful condition. The difficulties created by Burr have been obviated to a considerable extent through the punishment of acts ordinarily treasonable in nature under a different label, 19 within a formula provided by Chief Justice Marshall himself in Bollman. The passage reads:
Crimes so atrocious as those which have for their object the subversion by violence of those laws and those institutions which have been ordained in order to secure the peace and happiness of society, are not to escape punishment, because they have not ripened into treason. The wisdom of the legislature is competent to provide for the case; and the framers of our Constitution . . . must have conceived it more safe that punishment in such cases should be ordained by general laws, formed upon deliberation, under the influence of no resentments, and without knowing on whom they were to operate, than that it should be inflicted under the influence of those passions which the occasion seldom fails to excite, and which a flexible definition of the crime, or a construction which would render it flexible, might bring into operation. 20