With Sens. Rand Paul and Thom Tillis opposed to the package, GOP leaders can afford only one more defection. And multiple Republicans aren't yet sold on the measure.

The Senate on Monday morning began a "vote-a-rama" on proposed amendments to President Donald Trump's megabill for his second term priorities. It comes after a rare weekend session for senators, which included a dramatic 51-49 procedural vote on Saturday night to advance the massive tax and immigration bill and a forced reading of the 940-page bill by Democrats.

The outcome was not yet in sight. Senate Majority Leader John Thune of South Dakota acknowledged the Republicans are “figuring out how to get to the end game.”