Nearly two out of every three people signing up for health care coverage so far on Maryland's troubled insurance exchange qualified for Medicaid — helping the state top its goal for the program's enrollment. Enrolling more lower-income residents in the state and federal insurance program has been embraced by state leaders as a success amid all the exchange's difficulties. Launched Oct. 1 to offer Maryland's uninsured access to coverage, the exchange has been plagued by problems that state officials only recently said they mostly fixed — days before the deadline to sign up for coverage starting with the new year. The state has been expanding Medicaid coverage to more residents for years in an effort to reduce health care costs for all. Getting people into insurance is expected to help them better manage chronic conditions and to limit expensive visits to emergency rooms.