WASHINGTON — On the brink of defeat, Senate Majority Leader Mitch McConnell has kept alive the GOP promise of dismantling the Affordable Care Act by essentially telling fellow Republicans: it's this or nothing.

And after seven years of promises to end Obamacare, most Republicans don't want 'nothing.'

In fact, by Thursday afternoon Senate Republicans were lining up to support a new plan while openly hoping it never becomes law. Some were seeking assurances that if they vote for the latest proposal, the House would kill the plan. That's because they would prefer a House-Senate conference committee to come up with an entirely different version. To get there, the Senate has to pass something — anything — even a bill many are deriding.

"The worst possible outcome is to pass something that most of us believe is a placeholder and it becomes the final product," said Sen. Lindsey Graham (R., S.C.). "This placeholder concept, the 'skinny bill,' will destroy insurance markets and not even remotely replace Obamacare."

Still, he said he planned to vote for it if he has assurances that the House won't pass it and that his own health care proposal could be considered in the conference committee, which would aim to come up with yet another repeal and replace plan that both chambers would vote on.

He was hardly alone.

Sen. David Perdue (R., Ga.) told the Los Angeles Times that "The only possibly problem would be would the House take it up and actually have a vote on it." Sen. John McCain (R., Ariz.) said he's "very worried about it."

There is a risk, of course, that the House could, in fact, pass this bill and that President Trump might sign it into law. Senators were seeking promises that that won't happen.

But the so-called "skinny" repeal bill, expected to target a handful of Obamacare provisions, still had momentum — because Republicans want to keep the process alive, even if they have no idea what final bill they might ultimately vote on. The strategy is in keeping with how McConnell has inched toward the goal line, building pressure on GOP senators to not cast the vote that sinks the process.

With critical votes looming in the next 24 to 48, here's how the Senate endgame is shaping up, and what could come next.

The Skinny Repeal
The next big hurdle, probably Thursday or Friday, is an expected vote on the so-called "skinny repeal," a less sweeping rollback than earlier proposals — but one that would still carry major consequences and could re-open the door for a much broader repeal plan.

The idea is expected to come up at the end of what the Senate calls a "vote-a-rama," which is expected to begin Thursday and allows for an unlimited number of amendments on the pending health bill — the only cap being senators' stamina.

None of those votes, however, may ultimately matter.

In the end, perhaps late Thursday night or in the wee hours of Friday morning, McConnell will offer a final amendment that becomes the Senate bill. It'll basically wipe out all of the ideas that came before. It might incorporate some of the earlier amendments that proved popular, but doesn't have to.

Even now no one knows what that final bill will look like.

Plans that have leaked into news reports suggest it would primarily target some of Obamacare's most unpopular provisions. Possibilities include erasing mandates that most people carry health insurance and that businesses with 50 or more people offer coverage to their employees and axing a tax on medical-device makers. Planned Parenthood funding could be slashed. But even those ideas were in flux Thursday afternoon and could be changed.

Though the bill doesn't exist on paper — to Democrats' immense frustration — they asked for a CBO review of what's been floated. The nonpartisan analysts, according to Democrats, say it would increase the ranks of the uninsured by 16 million over the next decade and raise premiums for many by as much as 20 percent, contradicting one of Republicans' main goals in  repealing Obamacare: fighting rising premiums.

Democrats argue that the shorthand name skinny repeal belies big impacts.

Insurers have also warned that undoing the individual mandate would drive up prices. That's because healthy people would likely drop coverage and insurers would be left with a more expensive pool of customers. A handful of Republican governors, including those from Ohio and Nevada, denounced the GOP plan.

Republicans counter that the analysis of a non-existent bill is a sham, and have little problem with people who voluntarily decide to drop coverage, seeing that as their free choice.

The bill's fate is unclear — Republicans can afford to lose only two Senate votes and still pass it, and have encountered resistance at every turn. It would stop far short of the GOP pledges of the past seven years.

But it might be the option that offends the fewest Republicans and therefore has a chance to clear the Senate. It includes none of the Medicaid cuts that have deeply divided the party.

But that doesn't mean it would ultimately go to President Trump.

Trojan Horse?
For that to happen, the House would have to also adopt the skinny repeal.

The appeal in that move would be finally sending a bill to Trump, proclaiming victory and moving on to tax reform.

"It is better than nothing," Rep. Chris Collins (R., N.Y.), a close Trump ally, told the Washington Post. "I will support, I'll be honest, pretty much anything that comes over."

But such a narrow bill would disappoint conservatives who want Obamacare torn out by its roots and who hoped to use this opening for much more significant changes. Sen. Pat Toomey (R., Pa.), for example, has pushed a major overhaul of Medicaid funding. And conservatives hold significant sway in the House, giving them the power to potentially kill the skinny repeal and fight for something more.

Which brings us to the second option, the one most Senate Republicans are hoping for, even as they indicate they'll support the skinny bill: with the Senate and House having passed different bills, they could create a conference committee that could write an entirely new bill, one that could give new life to many of the ideas that the Senate has so far rejected.

The bill would go to both chambers for an up-or-down vote that would essentially be the final word on the repeal effort.

"That's a vehicle that's just meant to get us to conference," Toomey said of the skinny repeal Wednesday. ///On the Senate floor Thursday, he argued for restoring the Medicaid spending reductions he has pushed.

Numerous other Republicans echoed his words, saying they are just hoping to pass anything that keeps the process alive.

"It is not a solution to the Affordable Care Act problems," Sen. Lamar Alexander (R., Tenn.) said on the Senate floor Thursday morning, "but it is a solution to how we get to a place to where we can write a solution."

Democrats say the skinny repeal is therefore a Trojan horse for bringing much more sweeping, conservative provisions back to the Senate floor in yet another pressure-packed, take-it-or-leave-it vote.

Of course, significant challenges would remain.

If House and Senate Republicans already had a plan that could pass both chambers, they would have proposed it by now. The conference committee would still have to thread a very fine needle as they tried to come up with something that could please enough moderates and conservatives to pass.

But once the bill was introduced, the pressure would be on.

Republicans would again face a choice between voting for something that they might not like — but that kept their repeal pledge — or accepting failure.

Their effort has been on the verge of defeat several times so far. But with a Republican president, Senate and House that have all vowed to repeal and replace the ACA, they have incentive to keep it going.