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.

A marathon voting session on President Donald Trump’s sweeping domestic policy bill is underway in the Senate and has stretched overnight into the early hours of Tuesday morning after a weekend of negotiations and delays.

Thune is working with a tight 53 to 47 GOP majority in the upper chamber. Republican Sens. Rand Paul of Kentucky and Thom Tillis of North Carolina voted against debating the bill in the first place and are anticipated to likewise reject its final passage.