Unfortunately, even if the POI supports you, it doesn't mean you will always get in. I was in contact with a POI for two years about my research and he encouraged me to apply to work with him and said I was a good fit with his area of interest. He doesn't sit on the admissions committee. I got a generic letter this week saying that my application was unsuccessful because my research proposal doesn't fit into the long-term goals of the department. I was really stunned, to say the least. And the POI has gone silent. Sigh.