Treason is the act of betraying one's country. Someone who commits an act of treason is known as a traitor, and he has further committed the sin of treachery. The definition of traitorous "betrayal" is a thorny problem for any free society. Politics in a representative democracy have been understood in modern times to require a loyal opposition, which means that the concept cannot be too expansive or debate and the life of the mind generally will be chilled. By contrast, a totalitarian state can simply designate all opposition to the philosophy of the ruling party or the policies of the leader as "treason". However, in order for the executive branch to be able to fulfill its duty to protect the polity, it must retain the possibility of pursuing criminal sanctions against domestic enemies of the existing order, at least to the extent they use violence.
In the United States treason is a federal crime, the only crime provided for in the United States Constitution. It is defined as levying war against the United States, adhering to their enemies, or giving their enemies aid and comfort. <(U.S. Const. art. 3, section 3, cl. 1).   Where treason is made a crime under state statutes, the definitions often emphasize action directed against state government. ( Cal. Penal Code section 37---treason consists of levying war against the state, adhering to its enemies, or giving enemies aid and comfort). Should a current or future president commit treason, they must first be impeached by the House, then indicted by a vote of the Senate to be removed from office, and then prosecuted under the statute. Any holder of political office who is removed from office through the impeachment process is then barred from running from political office.   
It is generally understood that treason is a crime that threatens all citizens and calls for the harshest penalties, typically capital punishment. In medieval English law, 'high treason' was defined as the murder or attempted murder of the reigning monarchy, or attempts to usurp or overthrow them or pervert the natural succession of the throne. 'Petty treason' was the murder of a social superior, such as a servant killing his master or a knight murdering the lord he was expected to serve, but this term gradually fell out of use after the decline of the feudal system, and because such cases could also be tried simply as murder. Before the Glorious Revolution of 1688 (which ejected the House of Stuart and made the English government truly limited), high treason carried a penalty of beheading for the nobility and hanging, drawing and quartering for others, a process vividly depicted towards the end of the 1995 film Braveheart. A famous example of such an execution was that in 1605 of Guy Fawkes, a member of a failed conspiracy of Roman Catholics who sought to assassinate the Protestant King James I and his parliament. The British hanged traitors as late as the mid-20th century.
The U. S. Constitution defines treason as "levying war against the United States, or in adhering to their enemies, giving them aid and comfort." It also (copying an earlier English statute, the Statute of Edward III) requires that no conviction shall be had for this crime in the absence of the sworn testimony of two witnesses. The high point of treason prosecutions came under the administration of Woodrow Wilson, when the Espionage Act of 1917 and Sedition Act of 1918 were used to convict scores of Americans for treason based upon speeches against American participation in World War I. The Sedition Act was eventually repealed (although at least two sections of the Espionage Act remain in U. S. law) and the modern clear and present danger doctrine was formulated to determine when the U. S. or any state could resort to restricting First Amendment rights to free expression.
Treason prosecutions in the modern U. S. are exceedingly rare; although an al-Qaeda operative born in California was recently indicted, other U. S. citizens who have fought in Afghanistan on the Taliban side, notably John Walker Lindh and Yasser Esam Hamdi, were tried on lesser charges, and Hamdi is now a free man. This is in part because there were no treason prosecutions arising from the Cold War; even the Rosenbergs were tried and sentenced to death for espionage, the selling of secrets, which led their lawyers to complain that they were being treated more harshly than the average American traitor in World War II, only two of whom having been sentenced to death. Aldrich Ames, originally charged with treason after his spying for Russia during the Cold War was revealed, avoided prosecution for this charge by reaching a plea agreement to lesser charges, and is now serving a life sentence.
The decision not to charge the Rosenbergs with treason may stem from the fact the Cold War remained latent, instead of being formally declared by Congress. This would mean that the definition of "enemies" is actually more problematic than that of any other word in the Constitution's treason clause, since the Rosenbergs undoubtedly adhered to the Soviet Union and gave it 'aid and comfort'. Comparably, Jonathan Pollard was also charged with and convicted of espionage and sentenced to life imprisonmment for passing American secrets to Israel, a state usually described as a stalwart ally of the U. S. As with the Rosenbergs, there were loud protests, this time including calls for a Presidential pardon.
- For example, gathering opposition research or "dirt" on Hillary Clinton is not treason. Hillary Clinton is a private citizen. Hillary Clinton is neither the government of the United States nor the American people.