“The Roberts court declared this threat unconstitutional, finding that Washington could use the carrot (dangling new money) but not the stick (withdrawing old money). The states, when they initially signed up for Medicaid, could not have anticipated that Congress would one day enact a law that caused Medicaid to be ‘no longer a program to care for the neediest among us, but rather an element of a comprehensive national plan to provide universal health insurance coverage,’ the Court reasoned.”