"impotent rage" refers to a feeling of intense anger and frustration that is powerless and ineffective. It describes a strong emotion which cannot bring about any positive change or accomplish anything. Full definition
For two months he was tortured with such an agony as led him at times to gnash his teeth in impotent rage against God and man. (religion.blogs.cnn.com)
More likely, angry Muslims will temporarily back off to seethe in impotent rage until an opportune time for vengeance. (firstthings.com)
It helped that Ferguson was a hot news story, and people felt a sense of impotent rage over the shooting of yet another unarmed black man. (beyondyourblog.com)