What really has many state leaders worried is something called the "woodwork effect." When big parts of the health law go into force in 2014, they worry it will bring out of the woodwork the millions of people who are already eligible for Medicaid but aren't already enrolled. When some people look to see if they can get health insurance through one of the health exchanges, they may discover a cheaper option. But many of those people signing up for Medicaid won't be members of the newly eligible expansion group, whose bills will be largely paid by the federal government. They'll be regular old Medicaid beneficiaries, and states will have to pay up to half their costs.