The phrase "mutually reinforcing" implies that two things are supporting and strengthening each other. Some synonyms for this phrase are interconnected, interdependent, complementary, and mutually beneficial. When two things are interconnected, they are connected with each other in a way that influences each other's outcomes. When they are interdependent, they rely on each other for stability and success. When they are complementary, they enhance each other's qualities. And when they mutually benefit, they result in advantages for both parties involved. Regardless of the specific synonym used, the meaning remains the same: two things are working together to create positive and lasting effects.