IMHO when they take that US oath they are lying to the indels, the great satan.
Deception, Lying and Taqiyya
Does Islam permit Muslims to lie?
Muslim scholars teach that Muslims should generally be truthful to each other, unless the purpose of lying is to "smooth over differences." There are several forms of lying to non-believers that are permitted under certain circumstances, the best known being taqiyya. These circumstances are typically those that advance the cause of Islam - in some cases by gaining the trust of non-believers in order to draw out their vulnerability and defeat them.