It is a complex issue, but America has too many people with no health insurance at all now--they live without it until they get very sick and present at Emergency Rooms for very expensive care, which they cannot afford and thus don't pay for, and those cost then get shifted onto the backs of those who do have insurance. It is not a sensible system--anyone who has ever looked at it, left or right, agrees it needs fixing.
The problem is the most sensible fix would cost some very rich companies their livelyhood, and they are effective politcal opposition.