The Patient Protection and Affordable Care Act is working, but it will work even better with more money, says a left-leaning think-tank. Half a trillion dollars would do the trick.

"The ACA was passed under tight budgetary constraints given its ambitious coverage goals and it is essentially underfunded in multiple ways," argue Linda J. Blumberg and John Holahan of the Urban Institute. "This underfunding has implications for health care affordability for families, and it also means that administration of the law has been shortchanged."

One of the main challenges is the cost of health plans for low-income adults. While PPACA has spurred millions to sign up for health insurance, the costs of many PPACA plans may still be too high for some currently uninsured people to shoulder. In addition to high premiums, many plans demand a high level of cost-sharing in the form of deductibles or co-pays. Some people, suggests the report, may decide the insurance is simply not worth it.