Senate Republican leaders know that chances of passing their health bill are slim, that they depend on preserving some Obamacare tax hikes, and that they probably require flipping the vote of vulnerable Nevada Sen. Dean Heller.

Those assessments, from a GOP strategist familiar with Majority Leader Mitch McConnell's thinking, show how narrow a path awaits Senate Republicans when they return July 10 after a holiday week off. McConnell hasn't given up, the strategist said, but is unlikely to allow debate to extend past July 21.

"The odds for them getting 51 votes might be at best one in five," the strategist said, even allowing for McConnell's tactical skills. "There are limits to what he can do. He is not turning water into wine."

The leadership can afford to lose just two of the GOP caucus' 52 members, which would then allow Vice President Mike Pence to cast the tie-breaking 51st vote in favor. Calculations begin with the assumption that Rand Paul, the leader's Kentucky colleague, is virtually certain to vote no.

The libertarian-minded Paul, echoing Nebraska Sen. Ben Sasse and President Donald Trump, suggested Friday that lawmakers first pass a simple repeal of Obamacare, then, after that, legislation to replace it. Senate leaders reject that option out of hand.

"For better or worse, that ship has sailed," the strategist familiar with McConnell's thinking said.

A repeal-first strategy was considered and rejected by GOP leaders and Trump himself early this year. Among other things, returning to it now would probably preclude action on tax reform until 2019.