Other forms: enablers
An enabler is someone who makes it possible for something to happen — often, something negative or destructive. If your friend is trying to eat less sugar and you give him a bag of gummy bears every day, you're an enabler.
Enabler has both positive and negative meanings, but it's the negative definition that is most common. Still, you can call someone an enabler if they help make something happen, or enable it: "My favorite teacher was the enabler who paved the way for me to go to college." The bad kind of enabler often provides cover or excuses for someone else's self-destructive behavior, making it easier for it to continue.