While there was no surprise over the Supreme Court's decision Monday to review the 2010 health-care act's insurance mandate, supporters of the law are reeling over the justices' announcement that they will also consider a long-shot challenge to what many consider an even more central provision of the statute. That provision is the extension of Medicaid to cover a greater number of the poor. Twenty-six states say the expansion amounts to an unconstitutional coercion of state governments, which provide part of Medicaid's funding. "The decision on this issue is probably the most important the Supreme Court will be making on the Affordable Care Act," said Ronald Pollack, executive director of Families USA, a consumer advocacy group that backs the law, referring to the statute by a common shorthand.