Sometime on Tuesday, Senate Republicans will vote whether to start debate on a plan to overhaul American health care, without knowing exactly what is in that plan or, by extension, how it will change the lives of millions of Americans.

There are few, if any, comparable examples of a bill with such wide-reaching consequences, being voted on so abruptly, with so many critical questions left unanswered less than 24 hours before it is taken up.

Senate leaders are bent on holding a vote. But after the plan was drafted in secret, it now needs substantial revisions under the Senate budget rules. And yet the White House and GOP leadership insist on forcing members to vote on Tuesday.

It is an unprecedentedly opaque process to try to pass legislation that overhauls an industry worth more than $3 trillion, which would undercut a law that has extended health coverage to more than 20 million middle-class and low-income Americans in the past seven years.

The fate of Obamacare, arguably the most significant domestic policy passed in a generation, hangs in the balance. Medicaid, a pillar of the American safety net since Lyndon B. Johnson’s Great Society, could be fundamentally changed by the Senate bill, with federal spending capped permanently for a program that covers more than 70 million of the most vulnerable people in the country.

But as the vote approaches, there is no final text, no Congressional Budget Office score. Senate Republicans at least acknowledge the absurdity, if you ask them — this, coming from a party that spent seven years eviscerating Democrats for passing Obamacare in the quote-unquote dead of night.

“I’ll need to know what I’m going to vote on,” Sen. Ron Johnson (R-WI) told reporters Monday. “I’m not real happy with the process. I think you guys are more than aware of that.”

Yet Johnson and 49 other Republican senators might very well vote to start the debate Tuesday afternoon, despite not knowing what bill their leaders want to pass or whether the Obamacare repeal-and-replace plan they’ve been crafting for the past two months would even function.

That’s the bet McConnell is making: that the compulsion for Republicans to say they delivered on their promise to gut the 2010 health care law overrides any concerns about decorum. The entire argument in favor of opening debate has been reduced to: “Inaction is not an option.”

Senate Republicans don’t know which bill they’re starting debate on

Just hours before the vote, Republican senators knew full well that they didn’t know what they’d be asked to support.

“I would like to know more, as I’m sure all of you would too,” Sen. Lisa Murkowski (R-AK), a key swing vote, told reporters late Monday afternoon.

Would she be able to make a decision in the intervening hours? “We’ll find out.”

For starters, senators weren’t sure which bill their leadership was expecting to take up once debate began. There are two options:

The Better Care Reconciliation Act, drafted by Majority Leader Mitch McConnell (R-KY) and his staff, which scales back much of Obamacare while overhauling Medicaid. This is the repeal-and-replacement plan the Senate has been working on for months.

The Obamacare Repeal Reconciliation Act, which repeals the law’s spending but keeps its insurance regulations and doesn’t attempt to replace any of Obamacare. This is a version of the repeal bill that passed Congress in 2015 but was vetoed by then-President Barack Obama.

The ORRA would not pass if it were offered, as at least three Republican senators have said they wouldn’t support it. (Democrats would vote no en masse.) The CBO estimated that 32 million fewer Americans would have insurance in 2026 under the bill. But McConnell might bring it up anyway, to give conservatives a vote on clean repeal.

The BCRA, on the other hand, is still being tweaked with mere hours before the first vote. The current iteration would lead to 22 million fewer Americans having insurance 10 years from now and Medicaid spending being cut by $772 billion, compared with under Obamacare.

The main Senate bill hasn’t been finalized or fully analyzed

But the current version of the BCRA won’t be the final version. The Senate parliamentarian has deemed several key provisions in violation of the chamber’s budget rules, including a provision that is essential to the bill’s own internal policy logic. Those provisions could have sweeping effects on the functioning of the American health care system.

A six-month waiting period for people who have a lapse in health coverage — the Republican replacement for Obamacare’s individual mandate — does not comply with those rules, the parliamentarian has said, per Senate Democrats. Without it, insurers and outside experts have said the insurance market under the BCRA wouldn’t work. Only sick people would buy coverage, while healthy people would go without, which would drive up costs for insurers and in turn send premiums skyrocketing.

A host of other questions loom before Tuesday’s vote. Here’s a more complete list:

Which version of Ted Cruz’s proposal to allow insurance companies to sell non-Obamacare plans — as long as they also sell Obamacare plans — will be included in the bill?

Is the Cruz amendment even allowable under the Senate rules? Some experts doubt it would be.

Will provisions defunding Planned Parenthood and restricting federal tax subsidies from paying for plans that cover abortions survive the process? They were also found to be in violation of the Senate rules but could be rewritten.

Will a $200 billion Medicaid “wraparound” — intended to offset the repeal of Obamacare’s Medicaid expansion (though not completely), which covered 15 million of the poorest Americans — be added to the bill?

What are the CBO’s cost and coverage projections for BCRA once the above questions are answered?

“If we don’t know those things before we go in, you’re voting in a blind fashion. I think we need more information,” Sen. Rand Paul (R-KY) told reporters Monday, as he ticked through his own questions. “Should we go on to a bill we haven’t even scored?”

The whole Senate debate has been rushed and secretive

This half-blind dash is the climax of a two-month debate that has been shrouded in mystery. McConnell decided in May to draft the BCRA entirely in secret, with no public hearings or expert testimony.

They aren’t just repealing and replacing Obamacare, which they have promised for seven years to do. They are also overhauling Medicaid — ending the program’s days as an open-ended entitlement and instituting a federal spending cap. Over the next 20 years, the CBO projects that federal Medicaid spending would drop by 35 percent versus current law. States could be forced to cut benefits or enrollment in order to make up for those losses.

But not a single expert has testified before the Senate about the plan — a fact that even some Republicans find unfathomable.

“To do that without holding a single hearing on what the implications would be for some of our most vulnerable citizens, for our rural hospitals and our nursing homes, is not an approach that I can endorse, ” Sen. Susan Collins (R-ME), who will likely vote against any plan over those objections, said. “In my state, the implications of that give me great concern, particularly since we haven’t explored in a public hearing.”

Likewise, groups representing hospitals, doctors, and patients who have devastating diseases such as cancer and diabetes have not been given an opportunity to testify before the Senate about the bill. The entire health care industry, as well as patient groups, is opposed to the BCRA — and even insurance companies, which have been more supportive than the rest, have some significant concerns about some late additions, including the Cruz provision.

But Republican leaders are undaunted. The vote will be held Tuesday, McConnell announced on the Senate floor Monday afternoon. Other members of leadership almost toyed with reporters who sought clarity, noting that, technically speaking, leadership wouldn’t have to decide on what bill to vote on until 20 hours of debate on the Senate floor had gone by.

This is what Sen. John Barrasso (R-WY) told reporters Monday afternoon:

Barrasso says they don't have to decide what they are voting on after MTP until the 20 hours of debate is up — Nathaniel Weixel (@NateWeixel) July 24, 2017

It’s a heck of a way to overhaul a sixth of the economy. And it is the choice Republicans have made for themselves.