efficacious
having the power to produce a desired effect
"Effective," and "effectual" are synonyms of "efficacious," but each of these words has a slightly different connotation. "Efficacious" suggests possession of a special quality or virtue that makes it possible to achieve a result ("a detergent that is efficacious in removing grease"). "Effective" stresses the power to produce or the actual production of a particular effect ("an effective rebuttal"), while "effectual" suggests the accomplishment of a desired result, especially as viewed after the fact ("measures taken to reduce underage drinking have proved effectual").
Republican debate