Partly, it was cut short by the onslaught of behaviorism. Partly, it was eaten from within by debates over things like imageless thought. But setting aside these debates, the program was sidetracked by its focus on qualia rather than intentionality. However, there were some differences between James's approach to introspection. He believed that introspection was unreliable, and had to be checked by other means.
Every thought is owned by the person thinking it.
The breach from one mind to another is the greatest breach in nature. Each perception modifies the brain, so that while we may perceive the same object twice, the two perceptions are different. And even following sleep and anesthesia, which produce time-gaps, the consciousness afterwards is continuous with the consciousness before. Consciousness has no existence apart from its contents. Note, too, the emphasis on the function of consciousness.