The Ryan-Trump tag team, though, has little margin for error. Without the help of Democrats, they stand to lose about 20 Republican votes in the House and two votes in the Senate on this first go-around. That means buy-in from most of Mr. Trump’s rivals from the Republican presidential race — Sens. Rand Paul of Kentucky and Lindsey Graham of South Carolina, whom Mr. Trump branded as “lightweights”; Sen. Marco Rubio of Florida, dubbed “little Marco”; and Sen. Ted Cruz of Texas, whom he named “Lyin’ Ted.” While Mr. Rubio has said he is open to the bill that Mr....