Which word describes behavior intended to sabotage or weaken?

The term "undermining" specifically captures the essence of behavior that is intended to sabotage or weaken something. When someone undermines a person, project, or system, they engage in actions that gradually diminish strength, value, or effectiveness. This can include subtle actions or words that disrupt or weaken confidence, authority, or the foundation of a particular endeavor.

In contrast, the other choices convey positive actions or approaches. "Supportive" and "encouraging" both imply reinforcement and assistance, aimed at bolstering strength or confidence in a person or situation. "Reinforcing" similarly suggests adding support or strengthening the existing structure. Therefore, "undermining" is the only choice that reflects an intention to weaken or sabotage rather than support or enhance, making it the appropriate answer.