Sen. Debbie Stabenow’s retirement will end the career of a senator who’s known for taking up unflashy but critical health care issues like mental health policy and funding reauthorizations. Why it matters: Her departure means the Senate will lose one of its most effective mental health champions. The big picture: Stabenow, who chairs the Senate Finance health subcommittee, is an ardent mental health advocate and led many of the mental health provisions passed last month in the omnibus package. They included legislation to increase the mental health care workforce and to get Medicare coverage for mental health counselors and therapists. She also spearheaded the 2014 Excellence in Mental Health and…