The basis of the directive on security screening is reliability as a person: honesty, trustworthiness, integrity and loyalty to Canada. It covers anything that raises doubt about whether you're an honest and reliable person. Are you inclined to lie? Are you inclined to shade things in your favour? Do you have attachments to foreign nations? Is there reason to believe that when making a decision, you might prioritize another nation over Canada?
Anything that raises doubt is brought forward to the individual, and the security screening official has a conversation with them. Out of that determination, a decision is made by the department: Do we trust this person to be reliable and loyal? Sometimes it is a no, but usually it is a yes.