Source: https://www.dcsecurityclearanceconsultants.com/dod-adjudicative-elements.php

An applicant must be of unquestioned allegiance to the United States. Any reason to suspect otherwise creates doubt about the applicant’s willingness to safeguard classified national security information (CNSI). Allegiance is the loyalty that a citizen owes to his or her country. If allegiance to the United States is in doubt, an individual’s willingness to safeguard classified information is also in doubt.

There is considerable overlap between the Allegiance Guideline and the Foreign Influence and Foreign Preference Guidelines. It is principally an Allegiance issue when an American citizen uses force or violence in seeking to overthrow or influence the U.S. Government, prevent others from exercising their constitutional rights or to harm deliberately the United States. It is principally a Foreign Influence or Foreign Preference issue when an individual shows a preference for a foreign country, serves a foreign interest or is vulnerable to foreign influence that puts protected information at risk. Some cases are adjudicated under all three guidelines.