An amendment is under consideration that maybe, just maybe, could unlock the whole Senate Republican health bill. It might knock over the dominoes necessary for a deal, starting with regulations, moving to tax subsidies, and ending up with more cash for Medicaid and fewer tax cuts for the rich. It comes with big long-term risks for Americans who have high medical costs — and it could ultimately shift the burden of covering the uninsured further way from middle-class Americans who already have insurance, and more onto predominantly wealthy taxpayers. Its author? Sen. Ted Cruz of Texas. Senate conservatives have been...