But the measure was immediately imperiled when two Republican senators, moderate Susan Collins of Maine and conservative Rand Paul of Kentucky, announced they were not swayed — even on a procedural motion to take up the bill next week, a motion to proceed.

One more defection would doom the bill and jeopardize the Republicans' seven-year-old quest to dismantle the health law that is a pillar of President Barack Obama's legacy. In a sign that more could follow, two other Republican senators, Lindsey Graham of South Carolina and Bill Cassidy of Louisiana, unveiled their own alternative plan, just minutes before Senate leaders offered their latest.

Senator Shelley Moore Capito, Republican of West Virginia, expressed "serious concerns about the Medicaid provisions" in the latest draft, although she did not reject it.

But the measure was immediately imperiled when two Republican senators, moderate Susan Collins of Maine and conservative Rand Paul of Kentucky, announced they were not swayed — even on a procedural motion to take up the bill next week, a motion to proceed.