Only about half of the states have indicated that they will expand Medicaid under the law, a central ingredient for the goal of providing coverage to those now uninsured. Some people who acquire insurance under the law may have trouble obtaining treatment, because of a shortage of doctors and state-level “scope of practice” laws restricting the ability of others like nurse practitioners to step in.

Most challenging of all is persuading young, healthy Americans — the most profitable customers for insurance companies — to buy their “mandated” coverage next year, even though the penalty for not doing so is a modest $95. White House officials say this group’s participation in health insurance marketplaces is vital to their success because it will offset the cost of less-healthy customers…

“I don’t think the American people want to go back,” said Representative Steve Israel of New York, who is the chairman of the House Democrats’ committee. But Democrats say they cannot afford to be passive.

“We already know that, left to its own devices, this doesn’t end up in a good place,” said Mark Mellman, a Democratic pollster. “Anyone who thinks this issue is done is fooling themselves.”