U.S. Constitution - Article 3 Section 3
Article 3 - The Judicial Branch
Section 3 - Treason
Treason against the United States, shall consist only in levying War against them, or in adhering to their Enemies, giving them Aid and Comfort.
If the men who wrote the U.S. Constitution were confronted with a Major General who lied about being in the employ of a foreign power while serving the President, the Framers would have hanged him from the nearest tree.
Link: U.S. Constitution - Article 3 Section 3