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.

Senate Republicans hope they are hours away from passing their massive tax and immigration bill. But the outcome is far from certain.

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.”