walk a tightrope
Also, be on a tightrope. Take or be on a very precarious course, as in A university press must walk a tightrope to publish scholarly books and still make money, or The general was on a tightrope as to whether he should advance or retreat. This idiom transfers the balancing act performed by tightrope or high-wire acrobats to other concerns. [First half of 1900s]