In the next day or so, Senate Republicans are expected to take their first vote in a health care crusade that has consumed Congress for the past six months.

Nobody knows what they’re voting on. Nobody knows if it can pass. Nobody is even sure if the Senate’s plan to repeal and replace Obamacare, as a policy, can even work.

It is a bewildering state of affairs — and health insurance for millions of poor and middle-class Americans hangs in the balance.

Every path forward that Senate Majority Leader Mitch McConnell has floated appears to lack the necessary support of 50 Republicans. Nevertheless, Senate leaders are promising to vote within the next 36 hours, without a workable bill, a final Congressional Budget Office score, or perhaps even the votes to pass anything.

“Mitch McConnell is Doc Brown — ‘Where we're going, we don't need roads,’” a Republican health care lobbyist quipped on Monday morning, referencing the cinematic classic Back to the Future.

Confusion and uncertainty are the order of the day. But this, as best as we can tell, is what’s going on.

1) Nobody knows which health care bill the Senate is trying to pass

Senate Republicans currently have two health care bills.

One is the Better Care Reconciliation Act, the repeal-and-replacement plan that Republicans have been discussing and drafting in private for the past two months. That’s the health care bill you’ve been hearing about for most of the Senate debate. That bill would overhaul Medicaid, end Medicaid expansion, scale back assistance for people buying private coverage, and roll back some of Obamacare’s regulations. The result would be, according to the CBO, 22 million fewer Americans with insurance in 2026.

The other is the Obamacare Repeal Reconciliation Act, an updated version of 2015 legislation that repeals all funding for Obamacare’s insurance expansion but keeps its regulations on insurers. This bill would lead to 32 million fewer Americans having health coverage 10 years from now, according to the CBO.

Senate leadership hasn’t yet decided which bill they’re even trying to advance to. They are meeting Monday evening to chart a path forward for a vote they are planning to hold the very next day.

2) The vote tally is fluid, but both bills have a steep climb to passage

There are two critical votes that could happen this week. The first is called “the motion to proceed,” which simply opens up the debate on the Senate floor. Then at some point after that, there would be a vote on one of the Senate bills — or maybe both.

McConnell has an extraordinarily thin margin or error: 50 of the 52 Senate Republicans must back any bill for it to pass, with the 48 Democrats united against the GOP’s plans.

The ORRA seems dead. Three Senate Republicans have already said they won’t vote for the repeal-and-delay bill, and 10 more might join them when the time comes. McConnell might nonetheless put it up for a vote, to give conservatives the vote on clean repeal that they’ve been asking for and to show them that such a plan doesn’t have the support to pass.

The BCRA also appears short on votes. But repealing and replacing Obamacare probably has a more viable path to passage, though the legislation as written still has some huge policy and political problems. Some changes would undoubtedly be necessary to win over enough conservatives and moderates to get 50 votes — changes that have yet to be unveiled, just hours before the first expected Senate vote.

Further complicating things is Arizona Sen. John McCain’s health emergency. McCain’s absence, plus the likelihood that moderate Sen. Susan Collins (R-ME) will vote against any bill Republicans put forward, means that McConnell must bring every other Republican senator on board in order to pass anything.

One possible course for McConnell is promising a vote on both bills: the ORRA to appease conservatives and the BCRA to persuade the other moderates. But he would be asking his members to start debate without any certainty about what the final product will be or whether it can pass.

3) The BCRA, as written, can’t even work after new guidance from the Senate parliamentarian

The Senate’s budget rules blew a big hole in the Senate’s repeal-and-replace bill on Friday.

According to Democratic Sen. Bernie Sanders’s office, the Senate parliamentarian has said that the bill’s six-month waiting period for people who have a lapse in health coverage — the GOP’s replacement for the individual mandate — is not permissible.

The provision was considered necessary in order to encourage people to sign up for health insurance and keep the market stable. Without such a provision, experts fear the insurance market could be sent into a death spiral — only the sickest people, who cost insurers the most, buy coverage, and premiums and costs continue to rise. Health insurers and conservative policy experts have said some kind of enticement for people to enroll in coverage is necessary for the individual market to work under the bill.

That news came Friday, leaving Republican leaders just a few days to rewrite the provision in hopes of clearing the Senate’s Byrd Rule, which is supposed to limit the policies considered under “budget reconciliation” to those that directly affect the federal budget.

It is not at all clear that any tinkering can save the waiting period; outside experts have long said any similar policy would not survive the Byrd Rule. And without it, the Republican bill is tailor-made for a death spiral.

Other politically important policies — defunding Planned Parenthood and placing abortion restrictions on federal tax subsidies — were also deemed out of order under the Byrd Rule. Those provisions must be rewritten too; otherwise, social conservatives are likely to balk at the bill, which would doom it.

4) Last-minute dealmaking is still underway to woo moderate holdouts

Wavering senators, Trump administration officials, and Senate leaders have been negotiating over the past week, seeking a compromise to bridge the current divides in the GOP conference over the BCRA.

Medicaid has been a sticking point, particularly for a half-dozen senators who represent states that expanded the program under Obamacare. The Hill reported that Senate leaders are prepared to add $200 billion in funding to the bill for those states. That wouldn’t actually be enough to offset the $772 billion in Medicaid cuts, much of which results from ending the expansion, but maybe it would win their votes anyway.

Collins, the most moderate Senate Republican, might be unpersuadable no matter what. She is concerned about the Medicaid spending caps and the projected losses in insurance coverage. She told reporters last week that she couldn’t vote for a bill that capped Medicaid spending, especially one brought up without any public hearings.

Some of the conservative holdouts are tricky. Kentucky Sen. Rand Paul seems nearly ungettable: He staked his opposition on the $182 billion in stabilization funding, calling it an insurance bailout, and leadership would never remove that money from the bill.

Utah Sen. Mike Lee is unsatisfied with the version of a proposal by Texas Sen. Ted Cruz, allowing non-Obamacare plans back on the market. A technical change might be enough to win him over. The demands of Kansas Sen. Jerry Moran, another BCRA opponent, have been opaque throughout the debate, so it’s not clear how leadership can secure his support.

5) No last-minute changes can fix the projected coverage losses under the BCRA

A big part of the BCRA’s problem is the estimated 22 million fewer Americans who would have insurance if it became law. Republican leaders have been pouring money into the bill, hoping that the extra funding will assuage moderates who are worried about the projected increase in the uninsured and a dramatic rise in the out-of-pocket costs Americans must pay for their health care.

But there is a simple math-based reality: No amount of funding is going to save the bill, and most of the money would be used to fix problems the BCRA itself creates.

As I detailed in this piece, the Senate health care bill destabilizes the individual insurance market and slashes spending on Obamacare’s Medicaid expansion — and there just isn’t enough money available to make up for those changes.

The bill cuts more than $1 trillion in federal health insurance, and Senate leaders are prepared to add back only $400 billion or so. The result is still a cut in benefits for Americans affected by the changes, and millions more people becoming uninsured.

“The bill is pouring money into stability funding in an effort to offset destabilizing policy changes in the bill,” Caroline Pearson, senior vice president of Avalere Health, an independent consulting firm, said of the money for the private market. “However, the infusion of funding is insufficient to compensate.”

Or as Matt Fiedler at the Brookings Institution put it, discussing the Medicaid cuts: “It does not matter what combination of federal funding streams are used to deliver that money. It is impossible to overcome that basic arithmetic reality.”