“The Goldwater Institute’s lawsuit challenges IPAB’s very existence as an unlawful delegation of congressional power. Although most of the legal challenges to Obamacare have focused on the individual mandate to purchase government-prescribed health insurance, IPAB is no less central to the overall regulatory scheme. Many members of Congress voted for Obamacare only when convinced of the dubious premise that the law would constrain health-care costs. If IPAB is removed, the flimsy cost-containment rationale will disappear as well.”