The US Constitution Article 3 states that treason "…shall consist only in levying War against them [the United States], or in adhering to their Enemies, giving them Aid and Comfort." An enemy, according to Article 1, is a country or entity that the US Congress has declared war against. The definition of treason was deliberately very narrowly construed to avoid having political opponents use it against each other. Also given the First Amendment of the Bill of Rights which places no limits on freedom of speech, there exists a very wide playing field for critics of the Federal government to vent their anger at policies and politicians, which is just as it should be.
So what do you do when powerful forces inside the United States advance the interests of another nation without any regard for the damage that it does? George Washington in his Farewell Address touched on the issue, calling it a "passionate attachment" and observed that "Against the insidious wiles of foreign influence…the jealousy of a free people ought to be constantly awake; since history and experience prove that foreign influence is one of the most baneful foes of Republican Government."
It does not require any particular genius to realize that someone living in one country while favoring the interests of another is not a desirable citizen whether or not the label treason is applicable. Some nations have common interests but, by their very nature, countries are competitive and normally seek advantage for their own citizens. Or at least that is what citizens normally expect from their government even if it is not always forthcoming.