A patient presents with easy bruising, petechiae, and a prolonged bleeding time, but a normal prothrombin time. Which of the following coagulation disorders is most likely responsible for these findings?

The presentation of easy bruising, petechiae, and a prolonged bleeding time with a normal prothrombin time suggests a disorder affecting primary hemostasis, such as von Willebrand disease, which is characterized by a deficiency or dysfunction of von Willebrand factor.